User Manual

Published on February 2017 | Categories: Documents | Downloads: 57 | Comments: 0 | Views: 1300

of 115

Content

BERKELEY LOGO 6.0
Berkeley Logo User Manual

Brian Harvey

i

Short Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 Data Structure Primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3 Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 4 Arithmetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 5 Logical Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 6 Graphics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 7 Workspace Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 8 Control Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 9 Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 10 Error Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 11 Special Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 12 Internationalization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 1.2 1.3 1.4 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Getter/Setter Variable Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Entering and Leaving Logo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tokenization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 5 6

2

Data Structure Primitives . . . . . . . . . . . . . . . . . . . . . 9
Constructors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 sentence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 fput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 lput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 array. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 mdarray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 listtoarray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 arraytolist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 combine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 gensym . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2 Data Selectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ﬁrst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ﬁrsts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 last . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 butﬁrst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 butﬁrsts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 butlast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 mditem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 pick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 remove . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 remdup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 quoted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.3 Data Mutators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 setitem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 mdsetitem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 .setﬁrst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 .setbf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 .setitem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 push . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 pop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 queue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 dequeue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.1

iv 2.4

BERKELEY LOGO 6.0 Predicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . wordp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . listp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . arrayp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . emptyp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . equalp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . notequalp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . beforep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .eq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . memberp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . substringp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . numberp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vbarredp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ascii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . rawascii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . lowercase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . uppercase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . standout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . parse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . runparse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 14 14 14 14 14 15 15 15 15 16 16 16 16 16 16 16 17 17 17 17 17 18 18

3

Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Transmitters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . print . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . show . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Receivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . readlist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . readword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . readrawline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . readchar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . readchars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 File Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setpreﬁx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . preﬁx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . openread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . openwrite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . openappend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . openupdate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . close . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . allopen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . closeall. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . eraseﬁle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 19 19 19 20 20 20 20 20 21 21 21 22 22 22 22 22 23 23 23 23 23 23

v dribble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . nodribble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setwrite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . reader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . writer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setreadpos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setwritepos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . readpos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . writepos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . eofp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ﬁlep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Terminal Access. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . keyp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cleartext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setcursor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cursor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setmargins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . settextcolor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . increasefont . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . settextsize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . textsize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setfont . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 24 24 24 25 25 25 25 25 25 25 26 26 26 26 26 26 26 27 27 27 27 28 28

4

Arithmetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.1 Numeric Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . sum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . diﬀerence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . minus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . product . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . quotient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . remainder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . modulo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . int . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . round . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . sqrt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . exp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . log10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ln . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . sin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . radsin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . radcos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . arctan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . radarctan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iseq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 29 29 29 29 29 30 30 30 30 30 30 30 30 30 31 31 31 31 31 31 31

vi

BERKELEY LOGO 6.0 rseq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Numeric Predicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . lessp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . greaterp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . lessequalp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . greaterequalp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Random Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . random . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . rerandom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Print Formatting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Bitwise Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bitand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bitxor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bitnot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ashift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . lshift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 32 32 32 32 32 32 32 33 33 33 33 33 33 33 34 34 34

5

Logical Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 or . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 not . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

6

Graphics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Turtle Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . forward . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . back . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . left . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . right . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setpos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . sety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setheading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . home . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . arc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Turtle Motion Queries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xcor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ycor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . heading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . towards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . scrunch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Turtle and Window Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . showturtle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . hideturtle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . clean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 37 37 37 38 38 38 38 38 38 38 38 39 39 39 39 39 39 39 39 39 39 40 40

vii clearscreen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . wrap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . fence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ﬁll . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ﬁlled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . label . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setlabelheight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . textscreen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . fullscreen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . splitscreen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setscrunch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . refresh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . norefresh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Turtle and Window Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . shownp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . screenmode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . turtlemode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . labelsize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 Pen and Background Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pendown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . penup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . penpaint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . penerase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . penreverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setpencolor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setpalette . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setpensize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setpenpattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setpen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setbackground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 Pen Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pendownp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . penmode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pencolor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . palette . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pensize. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7 Saving and Loading Pictures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . savepict . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . loadpict . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . epspict . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 Mouse Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . mousepos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . clickpos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buttonp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . button . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 40 40 40 41 41 41 41 41 41 42 42 42 42 42 43 43 43 43 43 43 43 44 44 44 44 44 44 45 45 45 45 45 45 45 46 46 46 46 46 46 46 47 47 47 47 47 47

viii

BERKELEY LOGO 6.0

7

Workspace Management . . . . . . . . . . . . . . . . . . . . . . 49
Procedure Deﬁnition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . to . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . deﬁne . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . fulltext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . copydef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Variable Deﬁnition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . make . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . local . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . localmake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . thing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . global . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Property Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pprop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . gprop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . remprop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . plist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Workspace Predicates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . procedurep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . primitivep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . deﬁnedp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . namep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . plistp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Workspace Queries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buried . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . traced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . stepped . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . plists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . namelist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pllist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . arity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6 Workspace Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . po . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . poall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . popls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . popl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 49 49 50 51 51 51 51 51 51 52 52 52 52 53 53 53 53 53 53 53 53 54 54 54 54 54 54 54 54 55 55 55 55 55 55 55 56 56 56 56 56 56 57 57 57 57 57

ix 7.7 Workspace Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erpls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erpl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buryall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buryname . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . unbury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . unburyall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . unburyname . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buriedp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . trace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . untrace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . tracedp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . unstep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . steppedp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . editﬁle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edpls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edpl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . save. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . savel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cslsload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . seteditor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setlibloc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . setcslsloc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . sethelploc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . settemploc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . gc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .setsegmentsize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 57 58 58 58 58 58 58 59 59 59 59 59 59 60 60 60 60 60 60 61 61 61 62 62 62 62 62 62 62 63 63 63 63 64 64 64 64 64 64 65

x

BERKELEY LOGO 6.0

8

Control Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . run . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . runresult . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . repeat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . forever . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . repcount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . if . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ifelse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iftrue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iﬀalse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . catch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . throw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pause . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . continue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . wait . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bye . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .maybeoutput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . goto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . tag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ignore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ‘................................................................ for . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . do.while . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . while . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . do.until . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . until . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . case. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Template-based Iteration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . apply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . invoke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . foreach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . map.se . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ﬁlter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ﬁnd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . reduce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . crossmap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cascade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . cascade.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 67 67 67 67 67 68 68 68 68 68 68 69 69 69 69 70 70 70 71 71 71 71 72 72 72 72 73 73 73 73 74 74 74 76 76 76 77 77 78 78 78 79 79 81 81

xi

9

Macros . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
.macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .defmacro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . macrop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . macroexpand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 85 85 85

10 11

Error Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

10.1

Special Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
allowgetset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buttonact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . caseignoredp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . commandline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . fullprintp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . keyact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . loadnoisily . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . printdepthlimit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . printwidthlimit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . redefp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . unburyonedit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . usealternatenames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . logoversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . logoplatform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 89 89 89 89 90 90 90 90 90 91 91 91 91 91 91

12

Internationalization . . . . . . . . . . . . . . . . . . . . . . . . . . 93

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Chapter 1: Introduction

1

1 Introduction

1.1 Overview
Copyright c 1993 by the Regents of the University of California This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY ; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. This is a program that is still being written. Many things are missing, including adequate documentation. This manual assumes that you already know how to program in Logo, and merely presents the details of this new implementation. Read Computer Science Logo Style, Volume 1: Symbolic Computing by Brian Harvey (MIT Press, 1997) for a tutorial on Logo programming with emphasis on symbolic computation. Here are the special features of this dialect of Logo: Source ﬁle compatible among Unix, DOS, Windows, and Mac platforms. Random-access arrays. Variable number of inputs to user-deﬁned procedures. Mutators for list structure (dangerous). Pause on error, and other improvements to error handling. Comments and continuation lines; formatting is preserved when procedure deﬁnitions are saved or edited. Terrapin-style tokenization (e.g., [2+3] is a list with one member) but LCSI-style syntax (no special forms except TO). The best of both worlds. First-class instruction and expression templates (see APPLY). Macros.

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Features not found in Berkeley Logo include robotics, music, animation, parallelism, and multimedia. For those, buy a commercial version.

1.2 Getter/Setter Variable Syntax
Logo distinguishes procedures from variables. A procedure is a set of instructions to carry out some computation; a variable is a named container that holds a data value such as a number, word, list, or array. In traditional Logo syntax, a non-numeric word typed without punctuation represents a request to invoke the procedure named by that word. A word typed with a preceding quotation mark represents the word itself. For example, in the instruction PRINT FIRST "WORD the procedures named FIRST and PRINT are invoked, but the procedure named WORD is not invoked; the word W-O-R-D is the input to FIRST. What about variables? There are two things one can do with a variable: give it a value, and ﬁnd out its value. To give a variable a value, Logo provides the primitive procedure MAKE, which requires two inputs: the name of the variable and the new value to be assigned. The ﬁrst input, the name of the variable, is just a word, and if (as is almost always the case) the programmer wants to assign a value to a speciﬁc variable whose name is known in advance, that input is quoted, just as any known speciﬁc word would be: MAKE "MY.VAR FIRST "WORD gives the variable named MY.VAR the value W (the ﬁrst letter of WORD). To ﬁnd the value of a variable, Logo provides the primitive procedure THING, which takes a variable name as its input, and outputs the value of the accessible variable with that name. Thus PRINT THING "MY.VAR will print W (supposing the MAKE above has been done). Since ﬁnding the value of a speciﬁc, known variable name is such a common operation, Logo also provides an abbreviated notation that combines THING with quote: PRINT :MY.VAR The colon (which Logo old-timers pronounce "dots") replaces THING and " in the earlier version of the instruction. Newcomers to Logo often complain about the need for all this punctuation. In particular, Logo programmers who learned about dots and quotes without also learning about THING wonder why an instruction such as MAKE "NEW.VAR :OLD.VAR uses two diﬀerent punctuation marks to identify the two variables. (Having read the paragraphs above, you will understand that actually both variable names are quoted, but the procedure THING is invoked to ﬁnd the value of OLD.VAR, since it’s that value, not OLD.VAR’s

Chapter 1: Introduction

3

name, that MAKE needs to know. It wouldn’t make sense to ask for THING of NEW.VAR, since we haven’t given NEW.VAR a value yet.) Although Logo’s punctuation rules make sense once understood, they do form a barrier to entry for the Logo beginner. Why, then, couldn’t Logo be designed so that an unpunctuated word would represent a procedure if there is a procedure by that name, or a variable if there is a variable by that name? Then we could say PRINT MY.VAR and Logo would realize that MY.VAR is the name of a variable, not of a procedure. The traditional reason not to use this convention is that Logo allows the same word to name a procedure and a variable at the same time. This is most often important for words that name data types, as in the following procedure: TO PLURAL :WORD OUTPUT WORD :WORD "S END Here the name WORD is a natural choice for the input to PLURAL, since it describes the kind of input that PLURAL expects. Within the procedure, we use WORD to represent Logo’s primitive procedure that combines two input words to form a new, longer word; we use :WORD to represent the variable containing the input, whatever actual word is given when PLURAL is invoked. ? PRINT PLURAL "COMPUTER COMPUTERS However, if a Logo instruction includes an unquoted word that is not the name of a procedure, Logo could look for a variable of that name instead. This would allow a "punctuationless" Logo, provided that users who want to work without colons for variables choose variable names that are not also procedure names. What about assigning a value to a variable? Could we do without the quotation mark on MAKE’s ﬁrst input? Alas, no. Although the ﬁrst input to MAKE is usually a constant, known variable name, sometimes it isn’t, as in this example: TO INCREMENT :VAR MAKE :VAR (THING :VAR)+1 ; Note: it’s not "VAR here! END ? MAKE "X 5 ? INCREMENT "X ? PRINT :X 6 The procedure INCREMENT takes a variable name as its input and changes the value of that variable. In this example there are two variables; the variable whose name is VAR, and whose value is the word X; and the variable whose name is X and whose value changes from 5 to 6. Suppose we changed the behavior of MAKE so that it took the word after MAKE as the name of the variable to change; we would be unable to write INCREMENT:

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TO INCREMENT :VAR ; nonworking! MAKE VAR (THING VAR)+1 END This would assign a new value to VAR, not to X. What we can do is to allow an alternative to MAKE, a "setter" procedure for a particular variable. The notation will be ? SETFOO 7 ? PRINT FOO 7 SETFOO is a "setter procedure" that takes one input (in this case the input 7) and assigns its value to the variable named FOO. Berkeley Logo allows users to choose either the traditional notation, in which case the same name can be used both for a procedure and for a variable, or the getter/setter notation, in which variable FOO is set with SETFOO and examined with FOO, but the same name can’t be used for procedure and variable. Here is how this choice is allowed: Berkeley Logo uses traditional notation, with procedures distinct from variables. However, if there is a variable named AllowGetSet whose value is TRUE (which there is, by default, when Logo starts up), then if a Logo instruction refers to a nonexistent procedure (so that the error message "I don’t know how to ..." would result), Logo tries the following two steps: 1. If the name is at least four characters long, and the ﬁrst three characters are the letters SET (upper or lower case), and if the name is followed in the instruction by another value, and if the name without the SET is the name of a variable that already exists, then Logo will invoke MAKE with its ﬁrst input being the name without the SET, and its second input being the following value. 2. If step 1’s conditions are not met, but the name is the name of an accessible variable, then Logo will invoke THING with that name as input, to ﬁnd the variable’s value. Step 1 requires that the variable already exist so that misspellings of names of SETxxx primitives (e.g., SETHEADING) will still be caught, instead of silently creating a new variable. The command GLOBAL can be used to create a variable without giving it a value. One ﬁnal point: The TO command in Logo has always been a special case; the rest of the line starting with TO is not evaluated as ordinary Logo expressions are. In particular, the colons used to mark the names of inputs to the procedure do not cause THING to be invoked. They are merely mnemonic aids, reminding the Logo user that these words are names of variables. (Arguably, this nonstantard behavior of TO adds to Logo beginners’ confusion about colons.) To a programmer using colonless variable references, the colons in the TO line are unnecessary and meaningless. Berkeley Logo therefore makes the colons optional: TO FOO :IN1 :IN2

Chapter 1: Introduction

5

and TO FOO IN1 IN2 are both allowed.

1.3 Entering and Leaving Logo
The process to start Logo depends on your operating system: Unix: DOS: Mac: Type the word logo to the shell. (The directory in which you’ve installed Logo must be in your path.) Change directories to the one containing Logo (probably C:\UCBLOGO). Then type UCBLOGO for the large memory version, or BL for the 640K version. Double-click on the LOGO icon within the "UCB Logo" folder.

Windows: Double-click on the UCBWLOGO icon in the UCBLOGO folder. To leave Logo, enter the command bye. On startup, Logo looks for a ﬁle named ‘startup.lg’ in the system Logo library and, if found, loads it. Then it looks for ‘startup.lg’ in the user’s home directory, or the current directory, depending on the operating system, and loads that. These startup ﬁles can be used to predeﬁne procedures, e.g., to provide non-English names for primitive procedures. Under Unix, DOS, or Windows, if you include one or more ﬁlenames on the command line when starting Logo, those ﬁles will be loaded before the interpreter starts reading commands from your terminal. If you load a ﬁle that executes some program that includes a bye command, Logo will run that program and exit. You can therefore write standalone programs in Logo and run them with shell/batch scripts. To support this technique, Logo does not print its usual welcoming and parting messages if you give ﬁle arguments to the logo command. If a command line argument is just a hyphen, then all command line arguments after the hyphen are not taken as ﬁlenames, but are instead collected in a list, one word per argument; the buried variable COMMAND.LINE contains that list of arguments, or the empty list if there are none. On my Linux system, if the ﬁrst line of an executable shell script is #!/usr/local/bin/logo - (note the hyphen) then the script can be given command line arguments and they all end up in :COMMAND.LINE along with the script’s path. Experiment. If you type your interrupt character (see table below) Logo will stop what it’s doing and return to top-level, as if you did THROW "TOPLEVEL. If you type your quit character Logo will pause as if you did PAUSE. wxWidgets toplevel pause alt-S alt-P Unix usually ctrl-C usually ctrl-\ DOS/Windows ctrl-Q ctrl-W Mac Classic command-. (period) command-, (comma)

If you have an environment variable called LOGOLIB whose value is the name of a directory, then Logo will use that directory instead of the default library. If you invoke a procedure

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BERKELEY LOGO 6.0

that has not been deﬁned, Logo ﬁrst looks for a ﬁle in the current directory named ‘proc.lg’ where proc is the procedure name in lower case letters. If such a ﬁle exists, Logo loads that ﬁle. If the missing procedure is still undeﬁned, or if there is no such ﬁle, Logo then looks in the library directory for a ﬁle named ‘proc ’ (no ‘.lg’) and, if it exists, loads it. If neither ﬁle contains a deﬁnition for the procedure, then Logo signals an error. Several procedures that are primitive in most versions of Logo are included in the default library, so if you use a diﬀerent library you may want to include some or all of the default library in it.

1.4 Tokenization
Names of procedures, variables, and property lists are case-insensitive. So are the special words END, TRUE, and FALSE. Case of letters is preserved in everything you type, however. Within square brackets, words are delimited only by spaces and square brackets. [2+3] is a list containing one word. Note, however, that the Logo primitives that interpret such a list as a Logo instruction or expression (RUN, IF, etc.) reparse the list as if it had not been typed inside brackets. After a quotation mark outside square brackets, a word is delimited by a space, a square bracket, or a parenthesis. A word not after a quotation mark or inside square brackets is delimited by a space, a bracket, a parenthesis, or an inﬁx operator +-*/=<>. Note that words following colons are in this category. Note that quote and colon are not delimiters. Each inﬁx operator character is a word in itself, except that the two-character sequences <=, >=, and <> (the latter meaning not-equal) with no intervening space are recognized as a single word. A word consisting of a question mark followed by a number (e.g., ?37), when runparsed (i.e., where a procedure name is expected), is treated as if it were the sequence ( ? 37 ) making the number an input to the ? procedure. (See the discussion of templates, below.) This special treatment does not apply to words read as data, to words with a non-number following the question mark, or if the question mark is backslashed. A line (an instruction line or one read by READLIST or READWORD) can be continued onto the following line if its last character is a tilde (~). READWORD preserves the tilde and the newline; READLIST does not. Lines read with READRAWLINE are never continued. An instruction line or a line read by READLIST (but not by READWORD) is automatically continued to the next line, as if ended with a tilde, if there are unmatched brackets, parentheses, braces, or vertical bars pending. However, it’s an error if the continuation line contains only the word END; this is to prevent runaway procedure deﬁnitions. Lines explicitly continued with a tilde avoid this restriction. If a line being typed interactively on the keyboard is continued, either with a tilde or automatically, Logo will display a tilde as a prompt character for the continuation line.

Chapter 1: Introduction

7

A semicolon begins a comment in an instruction line. Logo ignores characters from the semicolon to the end of the line. A tilde as the last character still indicates a continuation line, but not a continuation of the comment. For example, typing the instruction print "abc;comment ~ def will print the word abcdef. Semicolon has no special meaning in data lines read by READWORD or READLIST, but such a line can later be reparsed using RUNPARSE and then comments will be recognized. The two-character sequence #! at the beginning of a line also starts a comment. Unix users can therefore write a ﬁle containing Logo commands, starting with the line #! /usr/local/bin/logo (or wherever your Logo executable lives) and the ﬁle will be executable directly from the shell. To include an otherwise delimiting character (including semicolon or tilde) in a word, precede it with backslash (\). If the last character of a line is a backslash, then the newline character following the backslash will be part of the last word on the line, and the line continues onto the following line. To include a backslash in a word, use \\. If the combination backslash-newline is entered at the terminal, Logo will issue a backslash as a prompt character for the continuation line. All of this applies to data lines read with READWORD or READLIST as well as to instruction lines. A line read with READRAWLINE has no special quoting mechanism; both backslash and vertical bar (described below) are just ordinary characters. An alternative notation to include otherwise delimiting characters in words is to enclose a group of characters in vertical bars. All characters between vertical bars are treated as if they were letters. In data read with READWORD the vertical bars are preserved in the resulting word. In data read with READLIST (or resulting from a PARSE or RUNPARSE of a word) the vertical bars do not appear explicitly; all potentially delimiting characters (including spaces, brackets, parentheses, and inﬁx operators) appear unmarked, but tokenized as though they were letters. Within vertical bars, backslash may still be used; the only characters that must be backslashed in this context are backslash and vertical bar themselves. Characters entered between vertical bars are forever special, even if the word or list containing them is later reparsed with PARSE or RUNPARSE. Characters typed after a backslash are treated somewhat diﬀerently: When a quoted word containing a backslashed character is runparsed, the backslashed character loses its special quality and acts thereafter as if typed normally. This distinction is important only if you are building a Logo expression out of parts, to be RUN later, and want to use parentheses. For example, PRINT RUN (SE "\( 2 "+ 3 "\)) will print 5, but RUN (SE "MAKE ""|(| 2)

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BERKELEY LOGO 6.0

will create a variable whose name is open-parenthesis. (Each example would fail if vertical bars and backslashes were interchanged.) A normally delimiting character entered within vertical bars is EQUALP to the same character without the vertical bars, but can be distinguished by the VBARREDP predicate. (However, VBARREDP returns TRUE only for characters for which special treatment is necessary: whitespace, parentheses, brackets, inﬁx operators, backslash, vertical bar, tilde, quote, question mark, colon, and semicolon.)

Chapter 2: Data Structure Primitives

9

2 Data Structure Primitives
2.1 Constructors
word
WORD word1 word2 (WORD word1 word2 word3 ...) outputs a word formed by concatenating its inputs.

list
LIST thing1 thing2 (LIST thing1 thing2 thing3 ...) outputs a list whose members are its inputs, which can be any Logo datum (word, list, or array).

sentence
SENTENCE thing1 thing2 SE thing1 thing2 (SENTENCE thing1 thing2 thing3 ...) (SE thing1 thing2 thing3 ...) outputs a list whose members are its inputs, if those inputs are not lists, or the members of its inputs, if those inputs are lists.

fput
FPUT thing list outputs a list equal to its second input with one extra member, the ﬁrst input, at the beginning. If the second input is a word, then the ﬁrst input must be a one-letter word, and FPUT is equivalent to WORD.

lput
LPUT thing list outputs a list equal to its second input with one extra member, the ﬁrst input, at the end. If the second input is a word, then the ﬁrst input must be a one-letter word, and LPUT is equivalent to WORD with its inputs in the other order.

array
ARRAY size (ARRAY size origin) outputs an array of size members (must be a positive integer), each of which initially is an empty list. Array members can be selected with ITEM and changed with SETITEM. The ﬁrst member of the array is member number 1 unless an origin input (must be an integer) is given, in which case the ﬁrst member of the array has that number as its index. (Typically

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BERKELEY LOGO 6.0

0 is used as the origin if anything.) Arrays are printed by PRINT and friends, and can be typed in, inside curly braces; indicate an origin with {a b c}@0. See [ITEM], page 12 , [SETITEM], page 12 , [PRINT], page 19 .

mdarray
MDARRAY sizelist (library procedure) (MDARRAY sizelist origin) outputs a multi-dimensional array. The ﬁrst input must be a list of one or more positive integers. The second input, if present, must be a single integer that applies to every dimension of the array. Ex: (MDARRAY [3 5] 0) outputs a two-dimensional array whose members range from [0 0] to [2 4].

listtoarray
LISTTOARRAY list (LISTTOARRAY list origin) outputs an array of the same size as the input list, whose members are the members of the input list.

arraytolist
ARRAYTOLIST array outputs a list whose members are the members of the input array. The ﬁrst member of the output is the ﬁrst member of the array, regardless of the array’s origin.

combine
COMBINE thing1 thing2 (library procedure) if thing2 is a word, outputs WORD thing1 thing2. FPUT thing1 thing2. See [WORD], page 9 , [FPUT], page 9 If thing2 is a list, outputs

reverse
REVERSE list (library procedure) outputs a list whose members are the members of the input list, in reverse order.

gensym
GENSYM (library procedure) outputs a unique word each time it’s invoked. The words are of the form G1, G2, etc.

2.2 Data Selectors
ﬁrst
FIRST thing

Chapter 2: Data Structure Primitives

11

if the input is a word, outputs the ﬁrst character of the word. If the input is a list, outputs the ﬁrst member of the list. If the input is an array, outputs the origin of the array (that is, the index of the ﬁrst member of the array).

ﬁrsts
FIRSTS list outputs a list containing the FIRST of each member of the input list. It is an error if any member of the input list is empty. (The input itself may be empty, in which case the output is also empty.) This could be written as to firsts :list output map "first :list end but is provided as a primitive in order to speed up the iteration tools MAP, MAP.SE, and FOREACH. to transpose :matrix if emptyp first :matrix [op []] op fput firsts :matrix transpose bfs :matrix end See [MAP], page 77 , [MAPdSE], page 77 , [FOREACH], page 76

last
LAST wordorlist if the input is a word, outputs the last character of the word. If the input is a list, outputs the last member of the list.

butﬁrst
BUTFIRST wordorlist BF wordorlist if the input is a word, outputs a word containing all but the ﬁrst character of the input. If the input is a list, outputs a list containing all but the ﬁrst member of the input.

butﬁrsts
BUTFIRSTS list BFS list outputs a list containing the BUTFIRST of each member of the input list. It is an error if any member of the input list is empty or an array. (The input itself may be empty, in which case the output is also empty.) This could be written as to butfirsts :list output map "butfirst :list end

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BERKELEY LOGO 6.0

but is provided as a primitive in order to speed up the iteration tools MAP, MAP.SE, and FOREACH. See [MAP], page 77 , [MAPdSE], page 77 , [FOREACH], page 76

butlast
BUTLAST wordorlist BL wordorlist if the input is a word, outputs a word containing all but the last character of the input. If the input is a list, outputs a list containing all but the last member of the input.

item
ITEM index thing if the thing is a word, outputs the indexth character of the word. If the thing is a list, outputs the indexth member of the list. If the thing is an array, outputs the indexth member of the array. Index starts at 1 for words and lists; the starting index of an array is speciﬁed when the array is created.

mditem
MDITEM indexlist array (library procedure) outputs the member of the multidimensional array selected by the list of numbers indexlist.

pick
PICK list (library procedure) outputs a randomly chosen member of the input list.

remove
REMOVE thing list (library procedure) outputs a copy of list with every member equal to thing removed.

remdup
REMDUP list (library procedure) outputs a copy of list with duplicate members removed. If two or more members of the input are equal, the rightmost of those members is the one that remains in the output.

quoted
QUOTED thing (library procedure) outputs its input, if a list; outputs its input with a quotation mark prepended, if a word.

2.3 Data Mutators
setitem
SETITEM index array value

Chapter 2: Data Structure Primitives

13

command. Replaces the indexth member of array with the new value. Ensures that the resulting array is not circular, i.e., value may not be a list or array that contains array.

mdsetitem
MDSETITEM indexlist array value (library procedure) command. Replaces the member of array chosen by indexlist with the new value.

.setﬁrst
.SETFIRST list value command. Changes the ﬁrst member of list to be value. WARNING: Primitives whose names start with a period are dangerous. Their use by nonexperts is not recommended. The use of .SETFIRST can lead to circular list structures, which will get some Logo primitives into inﬁnite loops, and to unexpected changes to other data structures that share storage with the list being modiﬁed.

.setbf
.SETBF list value command. Changes the butﬁrst of list to be value. WARNING: Primitives whose names start with a period are dangerous. Their use by non-experts is not recommended. The use of .SETBF can lead to circular list structures, which will get some Logo primitives into inﬁnite loops; unexpected changes to other data structures that share storage with the list being modiﬁed; or to Logo crashes and coredumps if the butﬁrst of a list is not itself a list.

.setitem
.SETITEM index array value command. Changes the indexth member of array to be value, like SETITEM, but without checking for circularity. WARNING: Primitives whose names start with a period are dangerous. Their use by nonexperts is not recommended. The use of .SETITEM can lead to circular arrays, which will get some Logo primitives into inﬁnite loops. See [SETITEM], page 12.

push
PUSH stackname thing (library procedure) command. Adds the thing to the stack that is the value of the variable whose name is stackname. This variable must have a list as its value; the initial value should be the empty list. New members are added at the front of the list.

pop
POP stackname (library procedure)

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BERKELEY LOGO 6.0

outputs the most recently PUSHed member of the stack that is the value of the variable whose name is stackname and removes that member from the stack.

queue
QUEUE queuename thing (library procedure) command. Adds the thing to the queue that is the value of the variable whose name is queuename. This variable must have a list as its value; the initial value should be the empty list. New members are added at the back of the list.

dequeue
DEQUEUE queuename (library procedure) outputs the least recently QUEUEd member of the queue that is the value of the variable whose name is queuename and removes that member from the queue.

2.4 Predicates
wordp
WORDP thing WORD? thing outputs TRUE if the input is a word, FALSE otherwise.

listp
LISTP thing LIST? thing outputs TRUE if the input is a list, FALSE otherwise.

arrayp
ARRAYP thing ARRAY? thing outputs TRUE if the input is an array, FALSE otherwise.

emptyp
EMPTYP thing EMPTY? thing outputs TRUE if the input is the empty word or the empty list, FALSE otherwise.

equalp
EQUALP thing1 thing2 EQUAL? thing1 thing2 thing1 = thing2 outputs TRUE if the inputs are equal, FALSE otherwise. Two numbers are equal if they have the same numeric value. Two non-numeric words are equal if they contain the same

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characters in the same order. If there is a variable named CASEIGNOREDP whose value is TRUE, then an upper case letter is considered the same as the corresponding lower case letter. (This is the case by default.) Two lists are equal if their members are equal. An array is only equal to itself; two separately created arrays are never equal even if their members are equal. (It is important to be able to know if two expressions have the same array as their value because arrays are mutable; if, for example, two variables have the same array as their values then performing SETITEM on one of them will also change the other.) See [CASEIGNOREDP], page 89 , [SETITEM], page 12

notequalp
NOTEQUALP thing1 thing2 NOTEQUAL? thing1 thing2 thing1 <> thing2 outputs FALSE if the inputs are equal, TRUE otherwise. See EQUALP for the meaning of equality for diﬀerent data types.

beforep
BEFOREP word1 word2 BEFORE? word1 word2 outputs TRUE if word1 comes before word2 in ASCII collating sequence (for words of letters, in alphabetical order). Case-sensitivity is determined by the value of CASEIGNOREDP. Note that if the inputs are numbers, the result may not be the same as with LESSP; for example, BEFOREP 3 12 is false because 3 collates after 1. See [CASEIGNOREDP], page 89 , [LESSP], page 32

.eq
.EQ thing1 thing2 outputs TRUE if its two inputs are the same datum, so that applying a mutator to one will change the other as well. Outputs FALSE otherwise, even if the inputs are equal in value. WARNING: Primitives whose names start with a period are dangerous. Their use by nonexperts is not recommended. The use of mutators can lead to circular data structures, inﬁnite loops, or Logo crashes.

memberp
MEMBERP thing1 thing2 MEMBER? thing1 thing2 if thing2 is a list or an array, outputs TRUE if thing1 is EQUALP to a member of thing2, FALSE otherwise. If thing2 is a word, outputs TRUE if thing1 is a one-character word EQUALP to a character of thing2, FALSE otherwise. See [EQUALP], page 14 .

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substringp
SUBSTRINGP thing1 thing2 SUBSTRING? thing1 thing2 if thing1 or thing2 is a list or an array, outputs FALSE. If thing2 is a word, outputs TRUE if thing1 is EQUALP to a substring of thing2, FALSE otherwise. See [EQUALP], page 14 .

numberp
NUMBERP thing NUMBER? thing outputs TRUE if the input is a number, FALSE otherwise.

vbarredp
VBARREDP char VBARRED? char BACKSLASHEDP char BACKSLASHED? char

(library procedure) (library procedure)

outputs TRUE if the input character was originally entered into Logo within vertical bars (|) to prevent its usual special syntactic meaning, FALSE otherwise. (Outputs TRUE only if the character is a backslashed space, tab, newline, or one of ()[]+-*/=<>":;\~?| ) The names BACKSLASHEDP and BACKSLASHED? are included in the Logo library for backward compatibility with the former names of this primitive, although it does not output TRUE for characters originally entered with backslashes.

2.5 Queries
count
COUNT thing outputs the number of characters in the input, if the input is a word; outputs the number of members in the input, if it is a list or an array. (For an array, this may or may not be the index of the last member, depending on the array’s origin.)

ascii
ASCII char outputs the integer (between 0 and 255) that represents the input character in the ASCII code. Interprets control characters as representing vbarred punctuation, and returns the character code for the corresponding punctuation character without vertical bars. (Compare RAWASCII.)

rawascii
RAWASCII char

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outputs the integer (between 0 and 255) that represents the input character in the ASCII code. Interprets control characters as representing themselves. To ﬁnd out the ASCII code of an arbitrary keystroke, use RAWASCII RC.

char
CHAR int outputs the character represented in the ASCII code by the input, which must be an integer between 0 and 255. See [ASCII], page 16 .

member
MEMBER thing1 thing2 if thing2 is a word or list and if MEMBERP with these inputs would output TRUE, outputs the portion of thing2 from the ﬁrst instance of thing1 to the end. If MEMBERP would output FALSE, outputs the empty word or list according to the type of thing2. It is an error for thing2 to be an array. See [MEMBERP], page 15 .

lowercase
LOWERCASE word outputs a copy of the input word, but with all uppercase letters changed to the corresponding lowercase letter.

uppercase
UPPERCASE word outputs a copy of the input word, but with all lowercase letters changed to the corresponding uppercase letter.

standout
STANDOUT thing outputs a word that, when printed, will appear like the input but displayed in standout mode (boldface, reverse video, or whatever your version does for standout). The word contains machine-speciﬁc magic characters at the beginning and end; in between is the printed form (as if displayed using TYPE) of the input. The output is always a word, even if the input is of some other type, but it may include spaces and other formatting characters. Note: a word output by STANDOUT while Logo is running on one machine will probably not have the desired eﬀect if printed on another type of machine. In the Macintosh classic version, the way that standout works is incompatible with the use of characters whose ASCII code is greater than 127. Therefore, you have a choice to make: The instruction CANINVERSE 0

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disables standout, but enables the display of ASCII codes above 127, and the instruction CANINVERSE 1 restores the default situation in which standout is enabled and the extra graphic characters cannot be printed.

parse
PARSE word outputs the list that would result if the input word were entered in response to a READLIST operation. That is, PARSE READWORD has the same value as READLIST for the same characters read. See [READLIST], page 20 , [READWORD], page 20

runparse
RUNPARSE wordorlist outputs the list that would result if the input word or list were entered as an instruction line; characters such as inﬁx operators and parentheses are separate members of the output. Note that sublists of a runparsed list are not themselves runparsed.

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3 Communication
3.1 Transmitters
Note: If there is a variable named PRINTDEPTHLIMIT with a nonnegative integer value, then complex list and array structures will be printed only to the allowed depth. That is, members of members of... of members will be allowed only so far. The members omitted because they are just past the depth limit are indicated by an ellipsis for each one, so a too-deep list of two members will print as [... ...]. If there is a variable named PRINTWIDTHLIMIT with a nonnegative integer value, then only the ﬁrst so many members of any array or list will be printed. A single ellipsis replaces all missing data within the structure. The width limit also applies to the number of characters printed in a word, except that a PRINTWIDTHLIMIT between 0 and 9 will be treated as if it were 10 when applied to words. This limit applies not only to the top-level printed datum but to any substructures within it. See [PRINTDEPTHLIMIT], page 90 , [PRINTWIDTHLIMIT], page 90 If there is a variable named FULLPRINTP whose value is TRUE, then words that were created using backslash or vertical bar (to include characters that would otherwise not be treated as part of a word) are printed with the backslashes or vertical bars shown, so that the printed result could be re-read by Logo to produce the same value. If FULLPRINTP is TRUE then the empty word (however it was created) prints as ||. (Otherwise it prints as nothing at all.) See [FULLPRINTP], page 90 .

print
PRINT thing PR thing (PRINT thing1 thing2 ...) (PR thing1 thing2 ...) command. Prints the input or inputs to the current write stream (initially the screen). All the inputs are printed on a single line, separated by spaces, ending with a newline. If an input is a list, square brackets are not printed around it, but brackets are printed around sublists. Braces are always printed around arrays.

type
TYPE thing (TYPE thing1 thing2 ...) command. Prints the input or inputs like PRINT, except that no newline character is printed at the end and multiple inputs are not separated by spaces. Note: printing to the screen is ordinarily line buﬀered; that is, the characters you print using TYPE will not actually appear on the screen until either a newline character is printed (for example, by PRINT or SHOW) or Logo tries to read from the keyboard (either at the request of your program or after an instruction prompt). This buﬀering makes the program much faster than it would be if each character appeared immediately, and in most cases the eﬀect is not disconcerting. To

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accommodate programs that do a lot of positioned text display using TYPE, Logo will force printing whenever SETCURSOR is invoked. This solves most buﬀering problems. Still, on occasion you may ﬁnd it necessary to force the buﬀered characters to be printed explicitly; this can be done using the WAIT command. WAIT 0 will force printing without actually waiting. See [SETCURSOR], page 26 , [WAIT], page 71

show
SHOW thing (SHOW thing1 thing2 ...) command. Prints the input or inputs like PRINT, except that if an input is a list it is printed inside square brackets. See [PRINT], page 19 .

3.2 Receivers
readlist
READLIST RL reads a line from the read stream (initially the keyboard) and outputs that line as a list. The line is separated into members as though it were typed in square brackets in an instruction. If the read stream is a ﬁle, and the end of ﬁle is reached, READLIST outputs the empty word (not the empty list). READLIST processes backslash, vertical bar, and tilde characters in the read stream; the output list will not contain these characters but they will have had their usual eﬀect. READLIST does not, however, treat semicolon as a comment character.

readword
READWORD RW reads a line from the read stream and outputs that line as a word. The output is a single word even if the line contains spaces, brackets, etc. If the read stream is a ﬁle, and the end of ﬁle is reached, READWORD outputs the empty list (not the empty word). READWORD processes backslash, vertical bar, and tilde characters in the read stream. In the case of a tilde used for line continuation, the output word does include the tilde and the newline characters, so that the user program can tell exactly what the user entered. Vertical bars in the line are also preserved in the output. Backslash characters are not preserved in the output.

readrawline
READRAWLINE reads a line from the read stream and outputs that line as a word. The output is a single word even if the line contains spaces, brackets, etc. If the read stream is a ﬁle, and the end of ﬁle is reached, READRAWLINE outputs the empty list (not the empty word). READRAWLINE

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outputs the exact string of characters as they appear in the line, with no special meaning for backslash, vertical bar, tilde, or any other formatting characters. See [READWORD], page 20 .

readchar
READCHAR RC reads a single character from the read stream and outputs that character as a word. If the read stream is a ﬁle, and the end of ﬁle is reached, READCHAR outputs the empty list (not the empty word). If the read stream is the keyboard, echoing is turned oﬀ when READCHAR is invoked, and remains oﬀ until READLIST or READWORD is invoked or a Logo prompt is printed. Backslash, vertical bar, and tilde characters have no special meaning in this context. See [READLIST], page 20 .

readchars
READCHARS num RCS num reads num characters from the read stream and outputs those characters as a word. If the read stream is a ﬁle, and the end of ﬁle is reached, READCHARS outputs the empty list (not the empty word). If the read stream is the keyboard, echoing is turned oﬀ when READCHARS is invoked, and remains oﬀ until READLIST or READWORD is invoked or a Logo prompt is printed. Backslash, vertical bar, and tilde characters have no special meaning in this context. See [READLIST], page 20 , [READWORD], page 20

shell
SHELL command (SHELL command wordflag) Under Unix, outputs the result of running command as a shell command. (The command is sent to ‘/bin/sh’, not ‘csh’ or other alternatives.) If the command is a literal list in the instruction line, and if you want a backslash character sent to the shell, you must use \\ to get the backslash through Logo’s reader intact. The output is a list containing one member for each line generated by the shell command. Ordinarily each such line is represented by a list in the output, as though the line were read using READLIST. If a second input is given, regardless of the value of the input, each line is represented by a word in the output as though it were read with READWORD. Example: to dayofweek output first first shell [date] end This is first first to extract the ﬁrst word of the ﬁrst (and only) line of the shell output. Under MacOS X, SHELL works as under Unix. SHELL is not available under Mac Classic.

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Under DOS, SHELL is a command, not an operation; it sends its input to a DOS command processor but does not collect the result of the command. Under Windows, the wxWidgets version of Logo behaves as under Unix (except that DOSstyle commands are understood; use dir rather than ls). The non-wxWidgets version behaves like the DOS version.

3.3 File Access
setpreﬁx
SETPREFIX string command. Sets a preﬁx that will be used as the implicit beginning of ﬁlenames in OPENREAD, OPENWRITE, OPENAPPEND, OPENUPDATE, LOAD, and SAVE commands. Logo will put the appropriate separator character (slash for Unix, backslash for DOS/Windows, colon for MacOS Classic) between the preﬁx and the ﬁlename entered by the user. The input to SETPREFIX must be a word, unless it is the empty list, to indicate that there should be no preﬁx. See [OPENREAD], page 22 , See [OPENWRITE], page 22 , See [OPENAPPEND], page 23 , See [OPENUPDATE], page 23 , See [LOAD], page 63 , See [SAVE], page 62 .

preﬁx
PREFIX outputs the current ﬁle preﬁx, or [] if there is no preﬁx. See [SETPREFIX], page 22 .

openread
OPENREAD filename command. Opens the named ﬁle for reading. The read position is initially at the beginning of the ﬁle.

openwrite
OPENWRITE filename command. Opens the named ﬁle for writing. If the ﬁle already existed, the old version is deleted and a new, empty ﬁle created. OPENWRITE, but not the other OPEN variants, will accept as input a two-element list, in which the ﬁrst element must be a variable name, and the second must be a positive integer. A character buﬀer of the speciﬁed size will be created. When a SETWRITE is done with this same list (in the sense of .EQ, not a copy, so you must do something like ? make "buf [foo 100] ? openwrite :buf ? setwrite :buf [...] ? close :buf

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and not just ? openwrite [foo 100] ? setwrite [foo 100] and so on), the printed characters are stored in the buﬀer; when a CLOSE is done with the same list as input, the characters from the buﬀer (treated as one long word, even if spaces and newlines are included) become the value of the speciﬁed variable.

openappend
OPENAPPEND filename command. Opens the named ﬁle for writing. If the ﬁle already exists, the write position is initially set to the end of the old ﬁle, so that newly written data will be appended to it.

openupdate
OPENUPDATE filename command. Opens the named ﬁle for reading and writing. The read and write position is initially set to the end of the old ﬁle, if any. Note: each open ﬁle has only one position, for both reading and writing. If a ﬁle opened for update is both READER and WRITER at the same time, then SETREADPOS will also aﬀect WRITEPOS and vice versa. Also, if you alternate reading and writing the same ﬁle, you must SETREADPOS between a write and a read, and SETWRITEPOS between a read and a write. See [READER], page 25 , [WRITER], page 25 , [SETREADPOS], page 25 , [SETWRITEPOS], page 25

close
CLOSE filename command. Closes the named ﬁle. If the ﬁle was currently the reader or writer, then the reader or writer is changed to the keyboard or screen, as if SETREAD [] or SETWRITE [] had been done.

allopen
ALLOPEN outputs a list whose members are the names of all ﬁles currently open. This list does not include the dribble ﬁle, if any.

closeall
CLOSEALL (library procedure) command. Closes all open ﬁles. Abbreviates FOREACH ALLOPEN [CLOSE ?] See [FOREACH], page 76 , [CLOSE], page 23

eraseﬁle
ERASEFILE filename

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ERF filename command. Erases (deletes, removes) the named ﬁle, which should not currently be open.

dribble
DRIBBLE filename command. Creates a new ﬁle whose name is the input, like OPENWRITE, and begins recording in that ﬁle everything that is read from the keyboard or written to the terminal. That is, this writing is in addition to the writing to WRITER. The intent is to create a transcript of a Logo session, including things like prompt characters and interactions. See [OPENWRITE], page 22 , [WRITER], page 25

nodribble
NODRIBBLE command. Stops copying information into the dribble ﬁle, and closes the ﬁle.

setread
SETREAD filename command. Makes the named ﬁle the read stream, used for READLIST, etc. The ﬁle must already be open with OPENREAD or OPENUPDATE. If the input is the empty list, then the read stream becomes the keyboard, as usual. Changing the read stream does not close the ﬁle that was previously the read stream, so it is possible to alternate between ﬁles. See [READLIST], page 20 , [OPENREAD], page 22 , [OPENUPDATE], page 23

setwrite
SETWRITE filename command. Makes the named ﬁle the write stream, used for PRINT, etc. The ﬁle must already be open with OPENWRITE, OPENAPPEND, or OPENUPDATE. If the input is the empty list, then the write stream becomes the screen, as usual. Changing the write stream does not close the ﬁle that was previously the write stream, so it is possible to alternate between ﬁles. If the input is a list, then its ﬁrst element must be a variable name, and its second and last element must be a positive integer; a buﬀer of that many characters will be allocated, and will become the writestream. If the same list (same in the .EQ sense, not a copy) has been used as input to OPENWRITE, then the already-allocated buﬀer will be used, and the writer can be changed to and from this buﬀer, with all the characters accumulated as in a ﬁle. When the same list is used as input to CLOSE, the contents of the buﬀer (as an unparsed word, which may contain newline characters) will become the value of the named variable. For compatibility with earlier versions, if the list has not been opened when the SETWRITE is done, it will be opened implicitly, but the ﬁrst SETWRITE after this one will implicitly close it, setting the variable and freeing the allocated buﬀer. See [PRINT], page 19 , [OPENWRITE], page 22 ; [OPENAPPEND], page 23 ; [OPENUPDATE], page 23

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reader
READER outputs the name of the current read stream ﬁle, or the empty list if the read stream is the terminal.

writer
WRITER outputs the name of the current write stream ﬁle, or the empty list if the write stream is the screen.

setreadpos
SETREADPOS charpos command. Sets the ﬁle pointer of the read stream ﬁle so that the next READLIST, etc., will begin reading at the charposth character in the ﬁle, counting from 0. (That is, SETREADPOS 0 will start reading from the beginning of the ﬁle.) Meaningless if the read stream is the keyboard. See [READLIST], page 20 .

setwritepos
SETWRITEPOS charpos command. Sets the ﬁle pointer of the write stream ﬁle so that the next PRINT, etc., will begin writing at the charposth character in the ﬁle, counting from 0. (That is, SETWRITEPOS 0 will start writing from the beginning of the ﬁle.) Meaningless if the write stream is the screen. See [PRINT], page 19 .

readpos
READPOS outputs the ﬁle position of the current read stream ﬁle.

writepos
WRITEPOS outputs the ﬁle position of the current write stream ﬁle.

eofp
EOFP EOF? predicate, outputs TRUE if there are no more characters to be read in the read stream ﬁle, FALSE otherwise.

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ﬁlep
FILEP filename FILE? filename (library procedure) predicate, outputs TRUE if a ﬁle of the speciﬁed name exists and can be read, FALSE otherwise.

3.4 Terminal Access
keyp
KEYP KEY? predicate, outputs TRUE if there are characters waiting to be read from the read stream. If the read stream is a ﬁle, this is equivalent to NOT EOFP. If the read stream is the terminal, then echoing is turned oﬀ and the terminal is set to cbreak (character at a time instead of line at a time) mode. It remains in this mode until some line-mode reading is requested (e.g., READLIST). The Unix operating system forgets about any pending characters when it switches modes, so the ﬁrst KEYP invocation will always output FALSE. See [EOFP], page 25 , [READLIST], page 20

cleartext
CLEARTEXT CT command. Clears the text window.

setcursor
SETCURSOR vector command. The input is a list of two numbers, the x and y coordinates of a text window position (origin in the upper left corner, positive direction is southeast). The text cursor is moved to the requested position. This command also forces the immediate printing of any buﬀered characters.

cursor
CURSOR outputs a list containing the current x and y coordinates of the text cursor. Logo may get confused about the current cursor position if, e.g., you type in a long line that wraps around or your program prints escape codes that aﬀect the screen strangely.

setmargins
SETMARGINS vector command. The input must be a list of two numbers, as for SETCURSOR. The eﬀect is to clear the screen and then arrange for all further printing to be shifted down and to the right according to the indicated margins. Speciﬁcally, every time a newline character is

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printed (explicitly or implicitly) Logo will type x margin spaces, and on every invocation of SETCURSOR the margins will be added to the input x and y coordinates. (CURSOR will report the cursor position relative to the margins, so that this shift will be invisible to Logo programs.) The purpose of this command is to accommodate the display of terminal screens in lecture halls with inadequate TV monitors that miss the top and left edges of the screen. See [SETCURSOR], page 26 .

settextcolor
SETTEXTCOLOR foreground background SETTC foreground background command (wxWidgets only). The inputs are color numbers, or RGB color lists, as for turtle graphics. The foreground and background colors for the textscreen/splitscreen text window are changed to the given values. The change aﬀects text already printed as well as future text printing; there is only one text color for the entire window. Command (non-wxWidgets Windows and DOS extended only). The inputs are color numbers, as for turtle graphics. Future printing to the text window will use the speciﬁed colors for foreground (the characters printed) and background (the space under those characters). Using STANDOUT will revert to the default text window colors. In the DOS extended (‘ucblogo.exe’) version, colors in textscreen mode are limited to numbers 0-7, and the coloring applies only to text printed by the program, not to the echoing of text typed by the user. Neither limitation applies to the text portion of splitscreen mode, which is actually drawn as graphics internally. See [STANDOUT], page 17 .

increasefont
INCREASEFONT DECREASEFONT command (wxWidgets only). Increase or decrease the size of the font used in the text and edit windows to the next larger or smaller available size.

settextsize
SETTEXTSIZE height command (wxWidgets only). Set the "point size" of the font used in the text and edit windows to the given integer input. The desired size may not be available, in which case the nearest available size will be used. Note: There is only a slight correlation between these integers and pixel sizes. Our rough estimate is that the number of pixels of height is about 1.5 times the point size, but it varies for diﬀerent fonts. See SETLABELHEIGHT for a diﬀerent approach used for the graphics window.

textsize
TEXTSIZE

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(wxWidgets only) outputs the "point size" of the font used in the text and edit windows. See SETTEXTSIZE for a discussion of font sizing. See LABELSIZE for a diﬀerent approach used for the graphics window.

setfont
SETFONT fontname command (wxWidgets only). Set the font family used in all windows to the one named by the input. Try ‘Courier’ or ‘Monospace’ as likely possibilities. Not all computers have the same fonts installed. It’s a good idea to stick with monospace fonts (ones in which all characters have the same width).

font
FONT (wxWidgets only) outputs the name of the font family used in all windows.

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4 Arithmetic
4.1 Numeric Operations
sum
SUM num1 num2 (SUM num1 num2 num3 ...) num1 + num2 outputs the sum of its inputs.

diﬀerence
DIFFERENCE num1 num2 num1 - num2 outputs the diﬀerence of its inputs. Minus sign means inﬁx diﬀerence in ambiguous contexts (when preceded by a complete expression), unless it is preceded by a space and followed by a nonspace. (See also MINUS.)

minus
MINUS num - num outputs the negative of its input. Minus sign means unary minus if the previous token is an inﬁx operator or open parenthesis, or it is preceded by a space and followed by a nonspace. There is a diﬀerence in binding strength between the two forms: MINUS 3 + 4 - 3 + 4 means means -(3+4) (-3)+4

product
PRODUCT num1 num2 (PRODUCT num1 num2 num3 ...) num1 * num2 outputs the product of its inputs.

quotient
QUOTIENT num1 num2 (QUOTIENT num) num1 / num2 outputs the quotient of its inputs. The quotient of two integers is an integer if and only if the dividend is a multiple of the divisor. (In other words, QUOTIENT 5 2 is 2.5, not 2, but QUOTIENT 4 2 is 2, not 2.0 — it does the right thing.) With a single input, QUOTIENT outputs the reciprocal of the input.

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remainder
REMAINDER num1 num2 outputs the remainder on dividing num1 by num2; both must be integers and the result is an integer with the same sign as num1.

modulo
MODULO num1 num2 outputs the remainder on dividing num1 by num2; both must be integers and the result is an integer with the same sign as num2.

int
INT num outputs its input with fractional part removed, i.e., an integer with the same sign as the input, whose absolute value is the largest integer less than or equal to the absolute value of the input.

round
ROUND num outputs the nearest integer to the input.

sqrt
SQRT num outputs the square root of the input, which must be nonnegative.

power
POWER num1 num2 outputs num1 to the num2 power. If num1 is negative, then num2 must be an integer.

exp
EXP num outputs e (2.718281828+) to the input power.

log10
LOG10 num outputs the common logarithm of the input.

ln
LN num outputs the natural logarithm of the input.

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sin
SIN degrees outputs the sine of its input, which is taken in degrees.

radsin
RADSIN radians outputs the sine of its input, which is taken in radians.

cos
COS degrees outputs the cosine of its input, which is taken in degrees.

radcos
RADCOS radians outputs the cosine of its input, which is taken in radians.

arctan
ARCTAN num (ARCTAN x y) outputs the arctangent, in degrees, of its input. With two inputs, outputs the arctangent of y/x, if x is nonzero, or 90 or –90 depending on the sign of y, if x is zero.

radarctan
RADARCTAN num (RADARCTAN x y) outputs the arctangent, in radians, of its input. With two inputs, outputs the arctangent of y/x, if x is nonzero, or pi/2 or –pi/2 depending on the sign of y, if x is zero. The expression 2*(RADARCTAN 0 1) can be used to get the value of pi.

iseq
ISEQ from to (library procedure) outputs a list of the integers from from to to, inclusive. ? show [3 4 5 ? show [7 6 5 iseq 3 7 6 7] iseq 7 3 4 3]

rseq
RSEQ from to count (library procedure) outputs a list of count equally spaced rational numbers between from and to, inclusive.

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? show rseq 3 5 9 [3 3.25 3.5 3.75 4 4.25 4.5 4.75 5] ? show rseq 3 5 5 [3 3.5 4 4.5 5]

4.2 Numeric Predicates
lessp
LESSP num1 num2 LESS? num1 num2 num1 < num2 outputs TRUE if its ﬁrst input is strictly less than its second.

greaterp
GREATERP num1 num2 GREATER? num1 num2 num1 > num2 outputs TRUE if its ﬁrst input is strictly greater than its second.

lessequalp
LESSEQUALP num1 num2 LESSEQUAL? num1 num2 num1 <= num2 outputs TRUE if its ﬁrst input is less than or equal to its second.

greaterequalp
GREATEREQUALP num1 num2 GREATEREQUAL? num1 num2 num1 >= num2 outputs TRUE if its ﬁrst input is greater than or equal to its second.

4.3 Random Numbers
random
RANDOM num (RANDOM start end) with one input, outputs a random nonnegative integer less than its input, which must be a positive integer. With two inputs, RANDOM outputs a random integer greater than or equal to the ﬁrst input, and less than or equal to the second input. Both inputs must be integers, and the ﬁrst must be less than the second. (RANDOM 0 9) is equivalent to RANDOM 10; (RANDOM 3 8) is equivalent to (RANDOM 6)+3.

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rerandom
RERANDOM (RERANDOM seed) command. Makes the results of RANDOM reproducible. Ordinarily the sequence of random numbers is diﬀerent each time Logo is used. If you need the same sequence of pseudo-random numbers repeatedly, e.g. to debug a program, say RERANDOM before the ﬁrst invocation of RANDOM. If you need more than one repeatable sequence, you can give RERANDOM an integer input; each possible input selects a unique sequence of numbers.

4.4 Print Formatting
form
FORM num width precision outputs a word containing a printable representation of num, possibly preceded by spaces (and therefore not a number for purposes of performing arithmetic operations), with at least width characters, including exactly precision digits after the decimal point. (If precision is 0 then there will be no decimal point in the output.) As a debugging feature, (FORM num -1 format) will print the ﬂoating point num according to the C printf format, to allow to hex :num op form :num -1 "|%08X %08X| end to allow ﬁnding out the exact result of ﬂoating point operations. The precise format needed may be machine-dependent.

4.5 Bitwise Operations
bitand
BITAND num1 num2 (BITAND num1 num2 num3 ...) outputs the bitwise and of its inputs, which must be integers. See [AND], page 35 .

bitor
BITOR num1 num2 (BITOR num1 num2 num3 ...) outputs the bitwise or of its inputs, which must be integers. See [OR], page 35 .

bitxor
BITXOR num1 num2

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(BITXOR num1 num2 num3 ...) outputs the bitwise exclusive or of its inputs, which must be integers. See [OR], page 35 .

bitnot
BITNOT num outputs the bitwise not of its input, which must be an integer. See [NOT], page 35 .

ashift
ASHIFT num1 num2 outputs num1 arithmetic-shifted to the left by num2 bits. If num2 is negative, the shift is to the right with sign extension. The inputs must be integers.

lshift
LSHIFT num1 num2 outputs num1 logical-shifted to the left by num2 bits. If num2 is negative, the shift is to the right with zero ﬁll. The inputs must be integers.

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5 Logical Operations
and
AND tf1 tf2 (AND tf1 tf2 tf3 ...) outputs TRUE if all inputs are TRUE, otherwise FALSE. All inputs must be TRUE or FALSE. (Comparison is case-insensitive regardless of the value of CASEIGNOREDP. That is, true or True or TRUE are all the same.) An input can be a list, in which case it is taken as an expression to run; that expression must produce a TRUE or FALSE value. List expressions are evaluated from left to right; as soon as a FALSE value is found, the remaining inputs are not examined. Example: MAKE "RESULT AND [NOT (:X = 0)] [(1 / :X) > .5] to avoid the division by zero if the ﬁrst part is false. See [CASEIGNOREDP], page 89 .

or
OR tf1 tf2 (OR tf1 tf2 tf3 ...) outputs TRUE if any input is TRUE, otherwise FALSE. All inputs must be TRUE or FALSE. (Comparison is case-insensitive regardless of the value of CASEIGNOREDP. That is, true or True or TRUE are all the same.) An input can be a list, in which case it is taken as an expression to run; that expression must produce a TRUE or FALSE value. List expressions are evaluated from left to right; as soon as a TRUE value is found, the remaining inputs are not examined. Example: IF OR :X=0 [some.long.computation] [...] to avoid the long computation if the ﬁrst condition is met. See [CASEIGNOREDP], page 89 .

not
NOT tf outputs TRUE if the input is FALSE, and vice versa. The input can be a list, in which case it is taken as an expression to run; that expression must produce a TRUE or FALSE value.

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6 Graphics
Berkeley Logo provides traditional Logo turtle graphics with one turtle. Multiple turtles, dynamic turtles, and collision detection are not supported. This is the most hardwaredependent part of Logo; some features may exist on some machines but not others. Nevertheless, the goal has been to make Logo programs as portable as possible, rather than to take fullest advantage of the capabilities of each machine. In particular, Logo attempts to scale the screen so that turtle coordinates [–100 –100] and [100 100] ﬁt on the graphics window, and so that the aspect ratio is 1:1. The center of the graphics window (which may or may not be the entire screen, depending on the machine used) is turtle location [0 0]. Positive X is to the right; positive Y is up. Headings (angles) are measured in degrees clockwise from the positive Y axis. (This diﬀers from the common mathematical convention of measuring angles counterclockwise from the positive X axis.) The turtle is represented as an isoceles triangle; the actual turtle position is at the midpoint of the base (the short side). However, the turtle is drawn one step behind its actual position, so that the display of the base of the turtle’s triangle does not obscure a line drawn perpendicular to it (as would happen after drawing a square). Colors are, of course, hardware-dependent. However, Logo provides partial hardware independence by interpreting color numbers 0 through 7 uniformly on all computers: 0 4 black red 1 5 blue magenta 2 6 green yellow 3 cyan 7 white

Where possible, Logo provides additional user-settable colors; how many are available depends on the hardware and operating system environment. If at least 16 colors are available, Logo tries to provide uniform initial settings for the colors 8-15: 8 12 brown salmon 9 13 tan purple 10 14 forest orange 11 15 aqua grey

Logo begins with a black background and white pen.

6.1 Turtle Motion
forward
FORWARD dist FD dist moves the turtle forward, in the direction that it’s facing, by the speciﬁed distance (measured in turtle steps).

back
BACK dist BK dist moves the turtle backward, i.e., exactly opposite to the direction that it’s facing, by the speciﬁed distance. (The heading of the turtle does not change.)

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left
LEFT degrees LT degrees turns the turtle counterclockwise by the speciﬁed angle, measured in degrees (1/360 of a circle).

right
RIGHT degrees RT degrees turns the turtle clockwise by the speciﬁed angle, measured in degrees (1/360 of a circle).

setpos
SETPOS pos moves the turtle to an absolute position in the graphics window. The input is a list of two numbers, the X and Y coordinates.

setxy
SETXY xcor ycor moves the turtle to an absolute position in the graphics window. The two inputs are numbers, the X and Y coordinates.

setx
SETX xcor moves the turtle horizontally from its old position to a new absolute horizontal coordinate. The input is the new X coordinate.

sety
SETY ycor moves the turtle vertically from its old position to a new absolute vertical coordinate. The input is the new Y coordinate.

setheading
SETHEADING degrees SETH degrees turns the turtle to a new absolute heading. The input is a number, the heading in degrees clockwise from the positive Y axis.

home
HOME moves the turtle to the center of the screen. Equivalent to SETPOS [0 0] SETHEADING 0. See [SETPOS], page 38 , See [SETHEADING], page 38 .

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arc
ARC angle radius draws an arc of a circle, with the turtle at the center, with the speciﬁed radius, starting at the turtle’s heading and extending clockwise through the speciﬁed angle. The turtle does not move.

6.2 Turtle Motion Queries
pos
POS outputs the turtle’s current position, as a list of two numbers, the X and Y coordinates.

xcor
XCOR (library procedure) outputs a number, the turtle’s X coordinate.

ycor
YCOR (library procedure) outputs a number, the turtle’s Y coordinate.

heading
HEADING outputs a number, the turtle’s heading in degrees.

towards
TOWARDS pos outputs a number, the heading at which the turtle should be facing so that it would point from its current position to the position given as the input.

scrunch
SCRUNCH outputs a list containing two numbers, the X and Y scrunch factors, as used by SETSCRUNCH. (But note that SETSCRUNCH takes two numbers as inputs, not one list of numbers.) See [SETSCRUNCH], page 42 .

6.3 Turtle and Window Control
showturtle
SHOWTURTLE ST makes the turtle visible.

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hideturtle
HIDETURTLE HT makes the turtle invisible. It’s a good idea to do this while you’re in the middle of a complicated drawing, because hiding the turtle speeds up the drawing substantially.

clean
CLEAN erases all lines that the turtle has drawn on the graphics window. The turtle’s state (position, heading, pen mode, etc.) is not changed.

clearscreen
CLEARSCREEN CS erases the graphics window and sends the turtle to its initial position and heading. Like HOME and CLEAN together. See [HOME], page 38 .

wrap
WRAP tells the turtle to enter wrap mode: From now on, if the turtle is asked to move past the boundary of the graphics window, it will "wrap around" and reappear at the opposite edge of the window. The top edge wraps to the bottom edge, while the left edge wraps to the right edge. (So the window is topologically equivalent to a torus.) This is the turtle’s initial mode. Compare WINDOW and FENCE. See [FENCE], page 40 .

window
WINDOW tells the turtle to enter window mode: From now on, if the turtle is asked to move past the boundary of the graphics window, it will move oﬀscreen. The visible graphics window is considered as just part of an inﬁnite graphics plane; the turtle can be anywhere on the plane. (If you lose the turtle, HOME will bring it back to the center of the window.) Compare WRAP and FENCE. See [HOME], page 38 .

fence
FENCE tells the turtle to enter fence mode: From now on, if the turtle is asked to move past the boundary of the graphics window, it will move as far as it can and then stop at the edge with an "out of bounds" error message. Compare WRAP and WINDOW.

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See [WRAP], page 40 .

ﬁll
FILL ﬁlls in a region of the graphics window containing the turtle and bounded by lines that have been drawn earlier. This is not portable; it doesn’t work for all machines, and may not work exactly the same way on diﬀerent machines.

ﬁlled
FILLED color instructions runs the instructions, remembering all points visited by turtle motion commands, starting and ending with the turtle’s initial position. Then draws (ignoring penmode) the resulting polygon, in the current pen color, ﬁlling the polygon with the given color, which can be a color number or an RGB list. The instruction list cannot include another FILLED invocation. (wxWidgets only)

label
LABEL text takes a word or list as input, and prints the input on the graphics window, starting at the turtle’s position.

setlabelheight
SETLABELHEIGHT height command (wxWidgets only). Takes a positive integer argument and tries to set the font size so that the character height (including descenders) is that many turtle steps. This will be diﬀerent from the number of screen pixels if SETSCRUNCH has been used. Also, note that SETSCRUNCH changes the font size to try to preserve this height in turtle steps. Note that the query operation corresponding to this command is LABELSIZE, not LABELHEIGHT, because it tells you the width as well as the height of characters in the current font.

textscreen
TEXTSCREEN TS rearranges the size and position of windows to maximize the space available in the text window (the window used for interaction with Logo). The details diﬀer among machines. Compare SPLITSCREEN and FULLSCREEN. See [SPLITSCREEN], page 42 .

fullscreen
FULLSCREEN FS rearranges the size and position of windows to maximize the space available in the graphics window. The details diﬀer among machines. Compare SPLITSCREEN and TEXTSCREEN.

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Since there must be a text window to allow printing (including the printing of the Logo prompt), Logo automatically switches from fullscreen to splitscreen whenever anything is printed. In the DOS version, switching from fullscreen to splitscreen loses the part of the picture that’s hidden by the text window. [This design decision follows from the scarcity of memory, so that the extra memory to remember an invisible part of a drawing seems too expensive.]

splitscreen
SPLITSCREEN SS rearranges the size and position of windows to allow some room for text interaction while also keeping most of the graphics window visible. The details diﬀer among machines. Compare TEXTSCREEN and FULLSCREEN. See [TEXTSCREEN], page 41 .

setscrunch
SETSCRUNCH xscale yscale adjusts the aspect ratio and scaling of the graphics display. After this command is used, all further turtle motion will be adjusted by multiplying the horizontal and vertical extent of the motion by the two numbers given as inputs. For example, after the instruction SETSCRUNCH 2 1 motion at a heading of 45 degrees will move twice as far horizontally as vertically. If your squares don’t come out square, try this. (Alternatively, you can deliberately misadjust the aspect ratio to draw an ellipse.) For all modern computers, both scale factors are initially 1. For DOS machines, the scale factors are initially set according to what the hardware claims the aspect ratio is, but the hardware sometimes lies. For DOS, the values set by SETSCRUNCH are remembered in a ﬁle (called ‘scrunch.dat’) and are automatically put into eﬀect when a Logo session begins.

refresh
REFRESH (command) tells Logo to remember the turtle’s motions so that they can be used for highresolution printing (wxWidgets) or to refresh the graphics window if it is moved, resized, or overlayed (non-wxWidgets). This is the default.

norefresh
NOREFRESH (command) tells Logo not to remember the turtle’s motions, which may be useful to save time and memory if your program is interactive or animated, rather than drawing a static picture you’ll want to print later (wxWidgets). In non-wxWidgets versions, using NOREFRESH may prevent Logo from restoring the graphics image after the window is moved, resized, or overlayed.

6.4 Turtle and Window Queries

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shownp
SHOWNP SHOWN? outputs TRUE if the turtle is shown (visible), FALSE if the turtle is hidden. See SHOWTURTLE and HIDETURTLE. See [SHOWTURTLE], page 39 , [HIDETURTLE], page 40 .

screenmode
SCREENMODE outputs the word TEXTSCREEN, SPLITSCREEN, or FULLSCREEN depending on the current screen mode.

turtlemode
TURTLEMODE outputs the word WRAP, FENCE, or WINDOW depending on the current turtle mode.

labelsize
LABELSIZE (wxWidgets only) outputs a list of two positive integers, the width and height of characters displayed by LABEL measured in turtle steps (which will be diﬀerent from screen pixels if SETSCRUNCH has been used). There is no SETLABELSIZE because the width and height of a font are not separately controllable, so the inverse of this operation is SETLABELHEIGHT, which takes just one number for the desired height.

6.5 Pen and Background Control
The turtle carries a pen that can draw pictures. At any time the pen can be UP (in which case moving the turtle does not change what’s on the graphics screen) or DOWN (in which case the turtle leaves a trace). If the pen is down, it can operate in one of three modes: PAINT (so that it draws lines when the turtle moves), ERASE (so that it erases any lines that might have been drawn on or through that path earlier), or REVERSE (so that it inverts the status of each point along the turtle’s path).

pendown
PENDOWN PD sets the pen’s position to DOWN, without changing its mode.

penup
PENUP PU sets the pen’s position to UP, without changing its mode.

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penpaint
PENPAINT PPT sets the pen’s position to DOWN and mode to PAINT.

penerase
PENERASE PE sets the pen’s position to DOWN and mode to ERASE. See [ERASE], page 57 .

penreverse
PENREVERSE PX sets the pen’s position to DOWN and mode to REVERSE. (This may interact in systemdependent ways with use of color.) See [REVERSE], page 10 .

setpencolor
SETPENCOLOR colornumber.or.rgblist SETPC colornumber.or.rgblist sets the pen color to the given number, which must be a nonnegative integer. There are initial assignments for the ﬁrst 16 colors: 0 4 8 12 black 1 blue 2 green 3 cyan red 5 magenta 6 yellow 7 white brown 9 tan 10 forest 11 aqua salmon 13 purple 14 orange 15 grey

but other colors can be assigned to numbers by the PALETTE command. Alternatively, sets the pen color to the given RGB values (a list of three nonnegative numbers less than 100 specifying the percent saturation of red, green, and blue in the desired color).

setpalette
SETPALETTE colornumber rgblist sets the actual color corresponding to a given number, if allowed by the hardware and operating system. Colornumber must be an integer greater than or equal to 8. (Logo tries to keep the ﬁrst 8 colors constant.) The second input is a list of three nonnegative numbers less than 100 specifying the percent saturation of red, green, and blue in the desired color.

setpensize
SETPENSIZE size

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sets the thickness of the pen. The input is either a single positive integer or a list of two positive integers (for horizontal and vertical thickness). Some versions pay no attention to the second number, but always have a square pen.

setpenpattern
SETPENPATTERN pattern sets hardware-dependent pen characteristics. This command is not guaranteed compatible between implementations on diﬀerent machines.

setpen
SETPEN list (library procedure) sets the pen’s position, mode, thickness, and hardware-dependent characteristics according to the information in the input list, which should be taken from an earlier invocation of PEN. See [PEN], page 46 .

setbackground
SETBACKGROUND colornumber.or.rgblist SETBG colornumber.or.rgblist set the screen background color by slot number or RGB values. See SETPENCOLOR for details. See [SETPENCOLOR], page 44 .

6.6 Pen Queries
pendownp
PENDOWNP PENDOWN? outputs TRUE if the pen is down, FALSE if it’s up.

penmode
PENMODE outputs one of the words PAINT, ERASE, or REVERSE according to the current pen mode. See [ERASE], page 57 , [REVERSE], page 10 .

pencolor
PENCOLOR PC outputs a color number, a nonnegative integer that is associated with a particular color, or a list of RGB values if such a list was used as the most recent input to SETPENCOLOR. There are initial assignments for the ﬁrst 16 colors: 0 black 1 blue 2 green 3 cyan

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4 8 12

red brown salmon

5 9 13

magenta tan purple

6 10 14

yellow forest orange

7 white 11 aqua 15 grey

but other colors can be assigned to numbers by the PALETTE command.

palette
PALETTE colornumber outputs a list of three nonnegative numbers less than 100 specifying the percent saturation of red, green, and blue in the color associated with the given number.

pensize
PENSIZE outputs a list of two positive integers, specifying the horizontal and vertical thickness of the turtle pen. (In some implementations, including wxWidgets, the two numbers are always equal.) PENPATTERN outputs system-speciﬁc pen information.

pen
PEN (library procedure) outputs a list containing the pen’s position, mode, thickness, and hardware-speciﬁc characteristics, for use by SETPEN. See [SETPEN], page 45 .

background
BACKGROUND BG outputs the graphics background color, either as a slot number or as an RGB list, whichever way it was set. (See PENCOLOR.)

6.7 Saving and Loading Pictures
savepict
SAVEPICT filename command. Writes a ﬁle with the speciﬁed name containing the state of the graphics window, including any nonstandard color palette settings, in Logo’s internal format. This picture can be restored to the screen using LOADPICT. The format is not portable between platforms, nor is it readable by other programs. [EPSPICT], page 47 to export Logo graphics for other programs.

loadpict
LOADPICT filename

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command. Reads the speciﬁed ﬁle, which must have been written by a SAVEPICT command, and restores the graphics window and color palette settings to the values stored in the ﬁle. Any drawing previously on the screen is cleared. See [SAVEPICT], page 46 .

epspict
EPSPICT filename command. Writes a ﬁle with the speciﬁed name, containing an Encapsulated Postscript (EPS) representation of the state of the graphics window. This ﬁle can be imported into other programs that understand EPS format. Restrictions: the drawing cannot use FILL, PENERASE, or PENREVERSE; any such instructions will be ignored in the translation to Postscript form. See [FILL], page 41 , See [PENERASE], page 44 , See [PENREVERSE], page 44 .

6.8 Mouse Queries
mousepos
MOUSEPOS outputs the coordinates of the mouse, provided that it’s within the graphics window, in turtle coordinates. If the mouse is outside the graphics window, then the last position within the window is returned. Exception: If a mouse button is pressed within the graphics window and held while the mouse is dragged outside the window, the mouse’s position is returned as if the window were big enough to include it.

clickpos
CLICKPOS outputs the coordinates that the mouse was at when a mouse button was most recently pushed, provided that that position was within the graphics window, in turtle coordinates. (wxWidgets only)

buttonp
BUTTONP BUTTON? outputs TRUE if a mouse button is down and the mouse is over the graphics window. Once the button is down, BUTTONP remains true until the button is released, even if the mouse is dragged out of the graphics window.

button
BUTTON outputs 0 if no mouse button has been pushed inside the Logo window since the last call to BUTTON. Otherwise, it outputs an integer between 1 and 3 indicating which button was most recently pressed. Ordinarily 1 means left, 2 means right, and 3 means center, but operating systems may reconﬁgure these.

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7 Workspace Management
7.1 Procedure Deﬁnition
to
TO procname :input1 :input2 ... (special form) command. Prepares Logo to accept a procedure deﬁnition. The procedure will be named procname and there must not already be a procedure by that name. The inputs will be called input1 etc. Any number of inputs are allowed, including none. Names of procedures and inputs are case-insensitive. Unlike every other Logo procedure, TO takes as its inputs the actual words typed in the instruction line, as if they were all quoted, rather than the results of evaluating expressions to provide the inputs. (That’s what special form means.) This version of Logo allows variable numbers of inputs to a procedure. After the procedure name come four kinds of things, in this order : 1. 2. 3. 4. 0 0 0 0 or or or or more REQUIRED inputs more OPTIONAL inputs 1 REST input 1 DEFAULT number :FOO :FROBOZZ [:BAZ 87] [:THINGO 5+9] [:GARPLY] 5

Every procedure has a minimum, default, and maximum number of inputs. (The latter can be inﬁnite.) The minimum number of inputs is the number of required inputs, which must come ﬁrst. A required input is indicated by the :inputname notation. After all the required inputs can be zero or more optional inputs, each of which is represented by the following notation: [:inputname default.value.expression] When the procedure is invoked, if actual inputs are not supplied for these optional inputs, the default value expressions are evaluated to set values for the corresponding input names. The inputs are processed from left to right, so a default value expression can be based on earlier inputs. Example: to proc :inlist [:startvalue first :inlist] If the procedure is invoked by saying proc [a b c] then the variable inlist will have the value [A B C] and the variable startvalue will have the value A. If the procedure is invoked by saying (proc [a b c] "x)

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then inlist will have the value [A B C] and startvalue will have the value X. After all the required and optional input can come a single rest input, represented by the following notation: [:inputname] This is a rest input rather than an optional input because there is no default value expression. There can be at most one rest input. When the procedure is invoked, the value of this inputname will be a list containing all of the actual inputs provided that were not used for required or optional inputs. Example: to proc :in1 [:in2 "foo] [:in3 "baz] [:in4] If this procedure is invoked by saying proc "x then in1 has the value X, in2 has the value FOO, in3 has the value BAZ, and in4 has the value [] (the empty list). If it’s invoked by saying (proc "a "b "c "d "e) then in1 has the value A, in2 has the value B, in3 has the value C, and in4 has the value [D E]. The maximum number of inputs for a procedure is inﬁnite if a rest input is given; otherwise, it is the number of required inputs plus the number of optional inputs. The default number of inputs for a procedure, which is the number of inputs that it will accept if its invocation is not enclosed in parentheses, is ordinarily equal to the minimum number. If you want a diﬀerent default number you can indicate that by putting the desired default number as the last thing on the TO line. example: to proc :in1 [:in2 "foo] [:in3] 3 This procedure has a minimum of one input, a default of three inputs, and an inﬁnite maximum. Logo responds to the TO command by entering procedure deﬁnition mode. The prompt character changes from ? to > and whatever instructions you type become part of the deﬁnition until you type a line containing only the word END.

deﬁne
DEFINE procname text command. Deﬁnes a procedure with name procname and text text. If there is already a procedure with the same name, the new deﬁnition replaces the old one. The text input must be a list whose members are lists. The ﬁrst member is a list of inputs; it looks like a TO line but without the word TO, without the procedure name, and without the colons before input names. In other words, the members of this ﬁrst sublist are words for the names of required inputs and lists for the names of optional or rest inputs. The remaining sublists of the text input make up the body of the procedure, with one sublist for each instruction line

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of the body. (There is no END line in the text input.) It is an error to redeﬁne a primitive procedure unless the variable REDEFP has the value TRUE. See [REDEFP], page 91 .

text
TEXT procname outputs the text of the procedure named procname in the form expected by DEFINE: a list of lists, the ﬁrst of which describes the inputs to the procedure and the rest of which are the lines of its body. The text does not reﬂect formatting information used when the procedure was deﬁned, such as continuation lines and extra spaces.

fulltext
FULLTEXT procname outputs a representation of the procedure procname in which formatting information is preserved. If the procedure was deﬁned with TO, EDIT, or LOAD, then the output is a list of words. Each word represents one entire line of the deﬁnition in the form output by READWORD, including extra spaces and continuation lines. The last member of the output represents the END line. If the procedure was deﬁned with DEFINE, then the output is a list of lists. If these lists are printed, one per line, the result will look like a deﬁnition using TO. Note: the output from FULLTEXT is not suitable for use as input to DEFINE! See [TO], page 49 , [EDIT], page 61 , [LOAD], page 63 , [DEFINE], page 50 .

copydef
COPYDEF newname oldname command. Makes newname a procedure identical to oldname. The latter may be a primitive. If newname was already deﬁned, its previous deﬁnition is lost. If newname was already a primitive, the redeﬁnition is not permitted unless the variable REDEFP has the value TRUE. Note: dialects of Logo diﬀer as to the order of inputs to COPYDEF. This dialect uses "MAKE order," not "NAME order." See [REDEFP], page 91 , [SAVE], page 62 , [PO], page 56 , [POT], page 57 .

7.2 Variable Deﬁnition
make
MAKE varname value command. Assigns the value value to the variable named varname, which must be a word. Variable names are case-insensitive. If a variable with the same name already exists, the value of that variable is changed. If not, a new global variable is created.

name
NAME value varname (library procedure) command. Same as MAKE but with the inputs in reverse order.

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local
LOCAL varname LOCAL varnamelist (LOCAL varname1 varname2 ...) command. Accepts as inputs one or more words, or a list of words. A variable is created for each of these words, with that word as its name. The variables are local to the currently running procedure. Logo variables follow dynamic scope rules; a variable that is local to a procedure is available to any subprocedure invoked by that procedure. The variables created by LOCAL have no initial value; they must be assigned a value (e.g., with MAKE) before the procedure attempts to read their value. See [MAKE], page 51 .

localmake
LOCALMAKE varname value (library procedure) command. Makes the named variable local, like LOCAL, and assigns it the given value, like MAKE. See [LOCAL], page 52 , See [MAKE], page 51 .

thing
THING varname :quoted.varname outputs the value of the variable whose name is the input. If there is more than one such variable, the innermost local variable of that name is chosen. The colon notation is an abbreviation not for THING but for the combination thing " so that :FOO means THING "FOO.

global
GLOBAL varname GLOBAL varnamelist (GLOBAL varname1 varname2 ...) command. Accepts as inputs one or more words, or a list of words. A global variable is created for each of these words, with that word as its name. The only reason this is necessary is that you might want to use the "setter" notation SETXYZ for a variable XYZ that does not already have a value; GLOBAL "XYZ makes that legal. Note: If there is currently a local variable of the same name, this command does *not* make Logo use the global value instead of the local one.

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7.3 Property Lists
Note: Names of property lists are always case-insensitive. Names of individual properties are case-sensitive or case-insensitive depending on the value of CASEIGNOREDP, which is TRUE by default. See [CASEIGNOREDP], page 89 . In principle, every possible name is the name of a property list, which is initially empty. So Logo never gives a "no such property list" error, as it would for undeﬁned procedure or variable names. But the primitive procedures that deal with "all" property lists (CONTENTS, PLISTS, etc.) list only nonempty ones. To "erase" a property list [ERASE], page 57 means to make it empty, removing all properties from it.

pprop
PPROP plistname propname value command. Adds a property to the plistname property list with name propname and value value.

gprop
GPROP plistname propname outputs the value of the propname property in the plistname property list, or the empty list if there is no such property.

remprop
REMPROP plistname propname command. Removes the property named propname from the property list named plistname.

plist
PLIST plistname outputs a list whose odd-numbered members are the names, and whose even-numbered members are the values, of the properties in the property list named plistname. The output is a copy of the actual property list; changing properties later will not magically change a list output earlier by PLIST.

7.4 Workspace Predicates
procedurep
PROCEDUREP name PROCEDURE? name outputs TRUE if the input is the name of a procedure.

primitivep
PRIMITIVEP name PRIMITIVE? name

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outputs TRUE if the input is the name of a primitive procedure (one built into Logo). Note that some of the procedures described in this document are library procedures, not primitives.

deﬁnedp
DEFINEDP name DEFINED? name outputs TRUE if the input is the name of a user-deﬁned procedure, including a library procedure.

namep
NAMEP name NAME? name outputs TRUE if the input is the name of a variable.

plistp
PLISTP name PLIST? name outputs TRUE if the input is the name of a nonempty property list. (In principle every word is the name of a property list; if you haven’t put any properties in it, PLIST of that name outputs an empty list, rather than giving an error message.)

7.5 Workspace Queries
Note: All procedures whose input is indicated as contentslist will accept a single word (taken as a procedure name), a list of words (taken as names of procedures), or a list of three lists as described under the CONTENTS command above.

contents
CONTENTS outputs a "contents list," i.e., a list of three lists containing names of deﬁned procedures, variables, and property lists respectively. This list includes all unburied named items in the workspace.

buried
BURIED outputs a contents list including all buried named items in the workspace.

traced
TRACED outputs a contents list including all traced named items in the workspace.

stepped
STEPPED

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outputs a contents list including all stepped named items in the workspace.

procedures
PROCEDURES outputs a list of the names of all unburied user-deﬁned procedures in the workspace. Note that this is a list of names, not a contents list. (However, procedures that require a contents list as input will accept this list.)

primitives
PRIMITIVES outputs a list of the names of all primitive procedures in the workspace. Note that this is a list of names, not a contents list. (However, procedures that require a contents list as input will accept this list.)

names
NAMES outputs a contents list consisting of an empty list (indicating no procedure names) followed by a list of all unburied variable names in the workspace.

plists
PLISTS outputs a contents list consisting of two empty lists (indicating no procedures or variables) followed by a list of all unburied nonempty property lists in the workspace.

namelist
NAMELIST varname (library procedure) NAMELIST varnamelist outputs a contents list consisting of an empty list followed by a list of the name or names given as input. This is useful in conjunction with workspace control procedures that require a contents list as input.

pllist
PLLIST plname (library procedure) PLLIST plnamelist outputs a contents list consisting of two empty lists followed by a list of the name or names given as input. This is useful in conjunction with workspace control procedures that require a contents list as input. See [CONTENTS], page 54 .

arity
ARITY procedurename

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outputs a list of three numbers: the minimum, default, and maximum number of inputs for the procedure whose name is the input. It is an error if there is no such procedure. A maximum of -1 means that the number of inputs is unlimited.

nodes
NODES outputs a list of two numbers. The ﬁrst represents the number of nodes of memory currently in use. The second shows the maximum number of nodes that have been in use at any time since the last invocation of NODES. (A node is a small block of computer memory as used by Logo. Each number uses one node. Each non-numeric word uses one node, plus some non-node memory for the characters in the word. Each array takes one node, plus some non-node memory, as well as the memory required by its elements. Each list requires one node per element, as well as the memory within the elements.) If you want to track the memory use of an algorithm, it is best if you invoke GC at the beginning of each iteration, since otherwise the maximum will include storage that is unused but not yet collected.

7.6 Workspace Inspection
po
PRINTOUT contentslist PO contentslist command. Prints to the write stream the deﬁnitions of all procedures, variables, and property lists named in the input contents list.

poall
POALL (library procedure) command. Prints all unburied deﬁnitions in the workspace. Abbreviates PO CONTENTS. See [CONTENTS], page 54 .

pops
POPS (library procedure) command. Prints the deﬁnitions of all unburied procedures in the workspace. Abbreviates PO PROCEDURES. See [PO], page 56 , [PROCEDURES], page 55 .

pons
PONS (library procedure) command. Prints the deﬁnitions of all unburied variables in the workspace. Abbreviates PO NAMES. See [PO], page 56 , [NAMES], page 55 .

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popls
POPLS (library procedure) command. Prints the contents of all unburied nonempty property lists in the workspace. Abbreviates PO PLISTS. See [PO], page 56 , [PLISTS], page 55 .

pon
PON varname (library procedure) PON varnamelist command. Prints the deﬁnitions of the named variable(s). Abbreviates PO NAMELIST varname(list). See [PO], page 56 , [NAMELIST], page 55 .

popl
POPL plname (library procedure) POPL plnamelist command. Prints the deﬁnitions of the named property list(s). Abbreviates PO PLLIST plname(list). See [PO], page 56 , [PLLIST], page 55 .

pot
POT contentslist command. Prints the title lines of the named procedures and the deﬁnitions of the named variables and property lists. For property lists, the entire list is shown on one line instead of as a series of PPROP instructions as in PO. See [PPROP], page 53 , [PO], page 56 .

pots
POTS (library procedure) command. Prints the title lines of all unburied procedures in the workspace. Abbreviates POT PROCEDURES. See [PROCEDURES], page 55 .

7.7 Workspace Control
erase
ERASE contentslist ER contentslist

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command. Erases from the workspace the procedures, variables, and property lists named in the input. Primitive procedures may not be erased unless the variable REDEFP has the value TRUE. See [REDEFP], page 91 .

erall
ERALL command. Erases all unburied procedures, variables, and property lists from the workspace. Abbreviates ERASE CONTENTS. See [CONTENTS], page 54 .

erps
ERPS command. Erases all unburied procedures from the workspace. Abbreviates ERASE PROCEDURES. See [ERASE], page 57 , [PROCEDURES], page 55 .

erns
ERNS command. Erases all unburied variables from the workspace. Abbreviates ERASE NAMES. See [ERASE], page 57 , [NAMES], page 55 .

erpls
ERPLS command. Erases all unburied property lists from the workspace. Abbreviates ERASE PLISTS. See [ERASE], page 57 , [PLISTS], page 55 .

ern
ERN varname (library procedure) ERN varnamelist command. Erases from the workspace the variable(s) named in the input. Abbreviates ERASE NAMELIST varname(list). See [ERASE], page 57 , [NAMELIST], page 55 .

erpl
ERPL plname (library procedure) ERPL plnamelist command. Erases from the workspace the property list(s) named in the input. Abbreviates ERASE PLLIST plname(list).

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See [ERASE], page 57 , [PLLIST], page 55 .

bury
BURY contentslist command. Buries the procedures, variables, and property lists named in the input. A buried item is not included in the lists output by CONTENTS, PROCEDURES, VARIABLES, and PLISTS, but is included in the list output by BURIED. By implication, buried things are not printed by POALL or saved by SAVE. See [CONTENTS], page 54 , [PROCEDURES], page 55 , [PONS], page 56 , [PLISTS], page 55 , [POALL], page 56 , [SAVE], page 62 .

buryall
BURYALL command. Abbreviates BURY CONTENTS. See [CONTENTS], page 54 . (library procedure)

buryname
BURYNAME varname (library procedure) BURYNAME varnamelist command. Abbreviates BURY NAMELIST varname(list). See [BURY], page 59 , [NAMELIST], page 55 .

unbury
UNBURY contentslist command. Unburies the procedures, variables, and property lists named in the input. That is, the named items will be returned to view in CONTENTS, etc. See [CONTENTS], page 54 .

unburyall
UNBURYALL (library procedure) command. Abbreviates UNBURY BURIED. See [BURIED], page 54 .

unburyname
UNBURYNAME varname (library procedure) UNBURYNAME varnamelist command. Abbreviates UNBURY NAMELIST varname(list) . See [UNBURY], page 59 , [NAMELIST], page 55 .

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buriedp
BURIEDP contentslist BURIED? contentslist outputs TRUE if the ﬁrst procedure, variable, or property list named in the contents list is buried, FALSE if not. Only the ﬁrst thing in the list is tested; the most common use will be with a word as input, naming a procedure, but a contents list is allowed so that you can BURIEDP [[] [variable ]] or BURIEDP [[] [] [proplist ]].

trace
TRACE contentslist command. Marks the named items for tracing. A message is printed whenever a traced procedure is invoked, giving the actual input values, and whenever a traced procedure STOPs or OUTPUTs. A message is printed whenever a new value is assigned to a traced variable using MAKE. A message is printed whenever a new property is given to a traced property list using PPROP. See [STOP], page 69 , [OUTPUT], page 69 , [MAKE], page 51 , [PPROP], page 53 .

untrace
UNTRACE contentslist command. Turns oﬀ tracing for the named items.

tracedp
TRACEDP contentslist TRACED? contentslist outputs TRUE if the ﬁrst procedure, variable, or property list named in the contents list is traced, FALSE if not. Only the ﬁrst thing in the list is tested; the most common use will be with a word as input, naming a procedure, but a contents list is allowed so that you can TRACEDP [[] [variable ]] or TRACEDP [[] [] [proplist ]].

step
STEP contentslist command. Marks the named items for stepping. Whenever a stepped procedure is invoked, each instruction line in the procedure body is printed before being executed, and Logo waits for the user to type a newline at the terminal. A message is printed whenever a stepped variable name is shadowed because a local variable of the same name is created either as a procedure input or by the LOCAL command. See [LOCAL], page 52 .

unstep
UNSTEP contentslist command. Turns oﬀ stepping for the named items.

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steppedp
STEPPEDP contentslist STEPPED? contentslist outputs TRUE if the ﬁrst procedure, variable, or property list named in the contents list is stepped, FALSE if not. Only the ﬁrst thing in the list is tested; the most common use will be with a word as input, naming a procedure, but a contents list is allowed so that you can STEPPEDP [[] [variable ]] or STEPPEDP [[] [] [proplist ]].

edit
EDIT contentslist ED contentslist (EDIT) (ED) command. If invoked with an input, EDIT writes the deﬁnitions of the named items into a temporary ﬁle and edits that ﬁle, using an editor that depends on the platform you’re using. In wxWidgets, and in the MacOS Classic version, there is an editor built into Logo. In the non-wxWidgets versions for Unix, MacOS X, Windows, and DOS, Logo uses your favorite editor as determined by the EDITOR environment variable. If you don’t have an EDITOR variable, edits the deﬁnitions using jove. If invoked without an input, EDIT edits the same ﬁle left over from a previous EDIT or EDITFILE instruction. When you leave the editor, Logo reads the revised deﬁnitions and modiﬁes the workspace accordingly. It is not an error if the input includes names for which there is no previous deﬁnition. If there is a variable LOADNOISILY whose value is TRUE, then, after leaving the editor, TO commands in the temporary ﬁle print ‘procname defined’ (where procname is the name of the procedure being deﬁned); if LOADNOISILY is FALSE or undeﬁned, TO commands in the ﬁle are carried out silently. If there is an environment variable called TEMP, then Logo uses its value as the directory in which to write the temporary ﬁle used for editing. Exceptionally, the EDIT command can be used without its default input and without parentheses provided that nothing follows it on the instruction line. See [LOADNOISILY], page 90 , See [EDITFILE], page 61 .

editﬁle
EDITFILE filename command. Starts the Logo editor, like EDIT, but instead of editing a temporary ﬁle it edits the ﬁle speciﬁed by the input. When you leave the editor, Logo reads the revised ﬁle, as for EDIT. EDITFILE also remembers the ﬁlename, so that a subsequent EDIT command with no input will re-edit the same ﬁle. EDITFILE is intended as an alternative to LOAD and SAVE. You can maintain a workspace ﬁle yourself, controlling the order in which deﬁnitions appear, maintaining comments in the ﬁle, and so on.

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In the wxWidgets version, EDITFILE asks whether or not you want to load the ﬁle into Logo when you ﬁnish editing. This allows you to use EDITFILE to edit data ﬁles without leaving Logo.

edall
EDALL (library procedure) command. Abbreviates EDIT CONTENTS. See [CONTENTS], page 54 .

edps
EDPS (library procedure) command. Abbreviates EDIT PROCEDURES. See [EDIT], page 61 , [PROCEDURES], page 55 .

edns
EDNS (library procedure) command. Abbreviates EDIT NAMES. See [EDIT], page 61 , [NAMES], page 55 .

edpls
EDPLS (library procedure) command. Abbreviates EDIT PLISTS. See [EDIT], page 61 , [PLISTS], page 55 .

edn
EDN varname (library procedure) EDN varnamelist command. Abbreviates EDIT NAMELIST varname(list) . See [EDIT], page 61 , [NAMELIST], page 55 .

edpl
EDPL plname (library procedure) EDPL plnamelist command. Abbreviates EDIT PLLIST plname(list) . See [EDIT], page 61 , [PLLIST], page 55 .

save
SAVE filename command. Saves the deﬁnitions of all unburied procedures, variables, and nonempty property lists in the named ﬁle. Equivalent to

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to save :filename local "oldwriter make "oldwriter writer openwrite :filename setwrite :filename poall setwrite :oldwriter close :filename end Exceptionally, SAVE can be used with no input and without parentheses if it is the last thing on the command line. In this case, the ﬁlename from the most recent LOAD or SAVE command will be used. (It is an error if there has been no previous LOAD or SAVE.)

savel
SAVEL contentslist filename (library procedure) command. Saves the deﬁnitions of the procedures, variables, and property lists speciﬁed by contentslist to the ﬁle named ﬁlename.

load
LOAD filename command. Reads instructions from the named ﬁle and executes them. The ﬁle can include procedure deﬁnitions with TO, and these are accepted even if a procedure by the same name already exists. If the ﬁle assigns a list value to a variable named STARTUP, then that list is run as an instructionlist after the ﬁle is loaded. If there is a variable LOADNOISILY whose value is TRUE, then TO commands in the ﬁle print ‘procname defined’ (where procname is the name of the procedure being deﬁned); if LOADNOISILY is FALSE or undeﬁned, TO commands in the ﬁle are carried out silently. See [STARTUP], page 91 , See [LOADNOISILY], page 90 .

cslsload
CSLSLOAD name command. Loads the named ﬁle, like LOAD, but from the directory containing the Computer Science Logo Style programs instead of the current user’s directory. See [LOAD], page 63 .

help
HELP name (HELP) command. Prints information from the reference manual about the primitive procedure named by the input. With no input, lists all the primitives about which help is available. If there is an environment variable LOGOHELP, then its value is taken as the directory in which to look for help ﬁles, instead of the default help directory.

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If HELP is called with the name of a deﬁned procedure for which there is no help ﬁle, it will print the title line of the procedure followed by lines from the procedure body that start with semicolon, stopping when a non-semicolon line is seen. Exceptionally, the HELP command can be used without its default input and without parentheses provided that nothing follows it on the instruction line.

seteditor
SETEDITOR path command. Tells Logo to use the speciﬁed program as its editor instead of the default editor. The format of a path depends on your operating system.

setlibloc
SETLIBLOC path command. Tells Logo to use the speciﬁed directory as its library instead of the default. (Note that many Logo "primitive" procedures are actually found in the library, so they may become unavailable if your new library does not include them!) The format of a path depends on your operating system.

setcslsloc
SETCSLSLOC path command. Tells Logo to use the speciﬁed directory for the CSLSLOAD command, instead of the default directory. The format of a path depends on your operating system. See [CSLSLOAD], page 63 .

sethelploc
SETHELPLOC path command. Tells Logo to look in the speciﬁed directory for the information provided by the HELP command, instead of the default directory. The format of a path depends on your operating system.

settemploc
SETTEMPLOC path command. Tells Logo to write editor temporary ﬁles in the speciﬁed directory rather than in the default directory. You must have write permission for this directory. The format of a path depends on your operating system.

gc
GC (GC anything) command. Runs the garbage collector, reclaiming unused nodes. Logo does this when necessary anyway, but you may want to use this command to control exactly when Logo does it. In particular, the numbers output by the NODES operation will not be very meaningful

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unless garbage has been collected. Another reason to use GC is that a garbage collection takes a noticeable fraction of a second, and you may want to schedule collections for times before or after some time-critical animation. If invoked with an argument (of any value), GC runs a full garbage collection, including GCTWA (Garbage Collect Truly Worthless Atoms, which means that it removes from Logo’s memory words that used to be procedure or variable names but aren’t any more); without an argument, GC does a generational garbage collection, which means that only recently created nodes are examined. (The latter is usually good enough.)

.setsegmentsize
.SETSEGMENTSIZE num command. Sets the number of nodes that Logo allocates from the operating system at once to num, which must be a positive integer. The name is dotted because bad things will happen if you use a number that’s too small or too large for your computer. The initial value is 16,000 for most systems, but is smaller for 68000-based Macs. Making it larger will speed up computations (by reducing the number of garbage collections) at the cost of allocating more memory than necessary.

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8 Control Structures
8.1 Control
Note: in the following descriptions, an instructionlist can be a list or a word. In the latter case, the word is parsed into list form before it is run. Thus, RUN READWORD or RUN READLIST will work. The former is slightly preferable because it allows for a continued line (with ~) that includes a comment (with ;) on the ﬁrst line. A tf input must be the word TRUE, the word FALSE, or a list. If it’s a list, then it must be a Logo expression, which will be evaluated to produce a value that must be TRUE or FALSE. The comparisons with TRUE and FALSE are always case-insensitive. A runlist can consist of either a single expression (that produces a value) or zero or more instructions (that do something, rather than output a value), depending on the context: PRINT IFELSE :X<0 ["NEGATIVE] ["POSITIVE] ; one value in each case REPEAT 4 [PRINT "A PRINT "B] ; two instructions

run
RUN instructionlist command or operation. Runs the Logo instructions in the input list; outputs if the list contains an expression that outputs. See [READWORD], page 20 , [READLIST], page 20 .

runresult
RUNRESULT instructionlist runs the instructions in the input; outputs an empty list if those instructions produce no output, or a list whose only member is the output from running the input instructionlist. Useful for inventing command-or-operation control structures: local "result make "result runresult [something] if emptyp :result [stop] output first :result

repeat
REPEAT num instructionlist command. Runs the instructionlist repeatedly, num times.

forever
FOREVER instructionlist command. Runs the "instructionlist" repeatedly, until something inside the instructionlist (such as STOP or THROW) makes it stop. See [STOP], page 69 , See [THROW], page 69 .

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repcount
REPCOUNT outputs the repetition count of the innermost current REPEAT or FOREVER, starting from 1. If no REPEAT or FOREVER is active, outputs –1. The abbreviation # can be used for REPCOUNT unless the REPEAT is inside the template input to a higher order procedure such as FOREACH, in which case # has a diﬀerent meaning.

if
IF tf instructionlist (IF tf instructionlist1 instructionlist2) command. If the ﬁrst input has the value TRUE, then IF runs the second input. If the ﬁrst input has the value FALSE, then IF does nothing. (If given a third input, IF acts like IFELSE, as described below.) It is an error if the ﬁrst input is not either TRUE or FALSE. For compatibility with earlier versions of Logo, if an IF instruction is not enclosed in parentheses, but the ﬁrst thing on the instruction line after the second input expression is a literal list (i.e., a list in square brackets), the IF is treated as if it were IFELSE, but a warning message is given. If this aberrant IF appears in a procedure body, the warning is given only the ﬁrst time the procedure is invoked in each Logo session.

ifelse
IFELSE tf instructionlist1 instructionlist2 command or operation. If the ﬁrst input has the value TRUE, then IFELSE runs the second input. If the ﬁrst input has the value FALSE, then IFELSE runs the third input. IFELSE outputs a value if the instructionlist contains an expression that outputs a value.

test
TEST tf command. Remembers its input, which must be TRUE or FALSE, for use by later IFTRUE or IFFALSE instructions. The eﬀect of TEST is local to the procedure in which it is used; any corresponding IFTRUE or IFFALSE must be in the same procedure or a subprocedure. See [IFFALSE], page 68 .

iftrue
IFTRUE instructionlist IFT instructionlist command. Runs its input if the most recent TEST instruction had a TRUE input. The TEST must have been in the same procedure or a superprocedure.

iﬀalse
IFFALSE instructionlist IFF instructionlist

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command. Runs its input if the most recent TEST instruction had a FALSE input. The TEST must have been in the same procedure or a superprocedure. See [TEST], page 68 .

stop
STOP command. Ends the running of the procedure in which it appears. Control is returned to the context in which that procedure was invoked. The stopped procedure does not output a value.

output
OUTPUT value OP value command. Ends the running of the procedure in which it appears. That procedure outputs the value value to the context in which it was invoked. Don’t be confused: OUTPUT itself is a command, but the procedure that invokes OUTPUT is an operation.

catch
CATCH tag instructionlist command or operation. Runs its second input. Outputs if that instructionlist outputs. If, while running the instructionlist, a THROW instruction is executed with a tag equal to the ﬁrst input (case-insensitive comparison), then the running of the instructionlist is terminated immediately. In this case the CATCH outputs if a value input is given to THROW. The tag must be a word. If the tag is the word ERROR, then any error condition that arises during the running of the instructionlist has the eﬀect of THROW "ERROR instead of printing an error message and returning to toplevel. The CATCH does not output if an error is caught. Also, during the running of the instructionlist, the variable ERRACT is temporarily unbound. (If there is an error while ERRACT has a value, that value is taken as an instructionlist to be run after printing the error message. Typically the value of ERRACT, if any, is the list [PAUSE].) See [ERROR], page 70 , [ERRACT], page 89 , [PAUSE], page 70 .

throw
THROW tag (THROW tag value) command. Must be used within the scope of a CATCH with an equal tag. Ends the running of the instructionlist of the CATCH. If THROW is used with only one input, the corresponding CATCH does not output a value. If THROW is used with two inputs, the second provides an output for the CATCH. THROW "TOPLEVEL can be used to terminate all running procedures and interactive pauses, and return to the toplevel instruction prompt. Typing the system interrupt character

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(ALT-S for wxWidgets; otherwise normally CONTROL-C for Unix, CONTROL-Q for DOS, or COMMAND-PERIOD for Mac) has the same eﬀect. THROW "ERROR can be used to generate an error condition. If the error is not caught, it prints a message (THROW "ERROR) with the usual indication of where the error (in this case the THROW) occurred. If a second input is used along with a tag of ERROR, that second input is used as the text of the error message instead of the standard message. Also, in this case, the location indicated for the error will be, not the location of the THROW, but the location where the procedure containing the THROW was invoked. This allows user-deﬁned procedures to generate error messages as if they were primitives. Note: in this case the corresponding CATCH "ERROR, if any, does not output, since the second input to THROW is not considered a return value. THROW "SYSTEM immediately leaves Logo, returning to the operating system, without printing the usual parting message and without deleting any editor temporary ﬁle written by EDIT. See [EDIT], page 61 .

error
ERROR outputs a list describing the error just caught, if any. If there was not an error caught since the last use of ERROR, the empty list will be output. The error list contains four members: an integer code corresponding to the type of error, the text of the error message (as a single word including spaces), the name of the procedure in which the error occurred, and the instruction line on which the error occurred.

pause
PAUSE command or operation. Enters an interactive pause. The user is prompted for instructions, as at toplevel, but with a prompt that includes the name of the procedure in which PAUSE was invoked. Local variables of that procedure are available during the pause. PAUSE outputs if the pause is ended by a CONTINUE with an input. If the variable ERRACT exists, and an error condition occurs, the contents of that variable are run as an instructionlist. Typically ERRACT is given the value [PAUSE] so that an interactive pause will be entered in the event of an error. This allows the user to check values of local variables at the time of the error. Typing the system quit character (ALT-S for wxWidgets; otherwise normally CONTROL-\ for Unix, CONTROL-W for DOS, or COMMAND-COMMA for Mac) will also enter a pause. See [ERRACT], page 89 .

continue
CONTINUE value CO value

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(CONTINUE) (CO) command. Ends the current interactive pause, returning to the context of the PAUSE invocation that began it. If CONTINUE is given an input, that value is used as the output from the PAUSE. If not, the PAUSE does not output. Exceptionally, the CONTINUE command can be used without its default input and without parentheses provided that nothing follows it on the instruction line.

wait
WAIT time command. Delays further execution for time 60ths of a second. Also causes any buﬀered characters destined for the terminal to be printed immediately. WAIT 0 can be used to achieve this buﬀer ﬂushing without actually waiting.

bye
BYE command. Exits from Logo; returns to the operating system.

.maybeoutput
.MAYBEOUTPUT value (special form) works like OUTPUT except that the expression that provides the input value might not, in fact, output a value, in which case the eﬀect is like STOP. This is intended for use in control structure deﬁnitions, for cases in which you don’t know whether or not some expression produces a value. Example: to invoke :function [:inputs] 2 .maybeoutput apply :function :inputs end ? (invoke "print "a "b "c) a b c ? print (invoke "word "a "b "c) abc This is an alternative to RUNRESULT. It’s fast and easy to use, at the cost of being an exception to Logo’s evaluation rules. (Ordinarily, it should be an error if the expression that’s supposed to provide an input to something doesn’t have a value.) See [OUTPUT], page 69 , [STOP], page 69 , [RUNRESULT], page 67 .

goto
GOTO word command. Looks for a TAG command with the same input in the same procedure, and continues running the procedure from the location of that TAG. It is meaningless to use GOTO outside of a procedure.

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tag
TAG quoted.word command. Does nothing. The input must be a literal word following a quotation mark ("), not the result of a computation. Tags are used by the GOTO command.

ignore
IGNORE value (library procedure) command. Does nothing. Used when an expression is evaluated for a side eﬀect and its actual value is unimportant.

‘
‘ list (library procedure) outputs a list equal to its input but with certain substitutions. If a member of the input list is the word ‘,’ (comma) then the following member should be an instructionlist that produces an output when run. That output value replaces the comma and the instructionlist. If a member of the input list is the word ‘,@’ (comma atsign) then the following member should be an instructionlist that outputs a list when run. The members of that list replace the ‘,@’ and the instructionlist. Example: show ‘[foo baz ,[bf [a b c]] garply ,@[bf [a b c]]] will print [foo baz [b c] garply b c] A word starting with ‘,’ or ‘,@’ is treated as if the rest of the word were a one-word list, e.g., ‘,:foo’ is equivalent to ‘,[:Foo]’. A word starting with ‘",’ (quote comma) or ‘:,’ (colon comma) becomes a word starting with ‘"’ or ‘:’ but with the result of running the substitution (or its ﬁrst word, if the result is a list) replacing what comes after the comma. Backquotes can be nested. Substitution is done only for commas at the same depth as the backquote in which they are found: ? show ‘[a ‘[b ,[1+2] ,[foo ,[1+3] d] e] f] [a ‘ [b , [1+2] , [foo 4 d] e] f] ?make "name1 "x ?make "name2 "y ? show ‘[a ‘[b ,:,:name1 ,",:name2 d] e] [a ‘ [b , [:x] , ["y] d] e]

for
FOR forcontrol instructionlist (library procedure) command. The ﬁrst input must be a list containing three or four members: (1) a word, which will be used as the name of a local variable; (2) a word or list that will be evaluated as

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by RUN to determine a number, the starting value of the variable; (3) a word or list that will be evaluated to determine a number, the limit value of the variable; (4) an optional word or list that will be evaluated to determine the step size. If the fourth member is missing, the step size will be 1 or –1 depending on whether the limit value is greater than or less than the starting value, respectively. The second input is an instructionlist. The eﬀect of FOR is to run that instructionlist repeatedly, assigning a new value to the control variable (the one named by the ﬁrst member of the forcontrol list) each time. First the starting value is assigned to the control variable. Then the value is compared to the limit value. FOR is complete when the sign of (current - limit) is the same as the sign of the step size. (If no explicit step size is provided, the instructionlist is always run at least once. An explicit step size can lead to a zero-trip FOR, e.g., FOR [I 1 0 1] ...). Otherwise, the instructionlist is run, then the step is added to the current value of the control variable and FOR returns to the comparison step. ? for [i 2 7 1.5] [print :i] 2 3.5 5 6.5 ? See [RUN], page 67 .

do.while
DO.WHILE instructionlist tfexpression (library procedure) command. Repeatedly evaluates the instructionlist as long as the evaluated tfexpres-sion remains TRUE. Evaluates the ﬁrst input ﬁrst, so the instructionlist is always run at least once. The tfexpression must be an expressionlist whose value when evaluated is TRUE or FALSE.

while
WHILE tfexpression instructionlist (library procedure) command. Repeatedly evaluates the instructionlist as long as the evaluated tfexpres-sion remains TRUE. Evaluates the ﬁrst input ﬁrst, so the instructionlist may never be run at all. The tfexpression must be an expressionlist whose value when evaluated is TRUE or FALSE.

do.until
DO.UNTIL instructionlist tfexpression (library procedure) command. Repeatedly evaluates the instructionlist as long as the evaluated tfexpres-sion remains FALSE. Evaluates the ﬁrst input ﬁrst, so the instructionlist is always run at least once. The tfexpression must be an expressionlist whose value when evaluated is TRUE or FALSE.

until
UNTIL tfexpression instructionlist (library procedure)

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command. Repeatedly evaluates the instructionlist as long as the evaluated tfexpres-sion remains FALSE. Evaluates the ﬁrst input ﬁrst, so the instructionlist may never be run at all. The tfexpression must be an expressionlist whose value when evaluated is TRUE or FALSE.

case
CASE value clauses (library procedure) command or operation. The second input is a list of lists (clauses); each clause is a list whose ﬁrst element is either a list of values or the word ELSE and whose butﬁrst is a Logo expression or instruction. CASE examines the clauses in order. If a clause begins with the word ELSE (upper or lower case), then the butﬁrst of that clause is evaluated and CASE outputs its value, if any. If the ﬁrst input to CASE is a member of the ﬁrst element of a clause, then the butﬁrst of that clause is evaluated and CASE outputs its value, if any. If neither of these conditions is met, then CASE goes on to the next clause. If no clause is satisﬁed, CASE does nothing. Example: to vowelp :letter output case :letter [ [[a e i o u] "true] [else "false] ] end

cond
COND clauses (library procedure) command or operation. The input is a list of lists (clauses); each clause is a list whose ﬁrst element is either an expression whose value is TRUE or FALSE, or the word ELSE, and whose butﬁrst is a Logo expression or instruction. COND examines the clauses in order. If a clause begins with the word ELSE (upper or lower case), then the butﬁrst of that clause is evaluated and CASE outputs its value, if any. Otherwise, the ﬁrst element of the clause is evaluated; the resulting value must be TRUE or FALSE. If it’s TRUE, then the butﬁrst of that clause is evaluated and COND outputs its value, if any. If the value is FALSE, then COND goes on to the next clause. If no clause is satisﬁed, COND does nothing. Example: to evens :numbers ; select even numbers from a list op cond [ [[emptyp :numbers] []] [[evenp first :numbers] ; assuming EVENP is defined fput first :numbers evens butfirst :numbers] [else evens butfirst :numbers] ] end

8.2 Template-based Iteration
The procedures in this section are iteration tools based on the idea of a template. This is a generalization of an instruction list or an expression list in which slots are provided for the tool to insert varying data. Four diﬀerent forms of template can be used. The most commonly used form for a template is ‘explicit-slot’ form, or ‘question mark’ form. Example: ? show map [? * ?] [2 3 4 5] [4 9 16 25]

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? In this example, the MAP tool evaluated the template [? * ?] repeatedly, with each of the members of the data list [2 3 4 5] substituted in turn for the question marks. The same value was used for every question mark in a given evaluation. Some tools allow for more than one datum to be substituted in parallel; in these cases the slots are indicated by ?1 for the ﬁrst datum, ?2 for the second, and so on: ? show (map [(word ?1 ?2 ?1)] [a b c] [d e f]) [ada beb cfc] ? If the template wishes to compute the datum number, the form (? 1) is equivalent to ?1, so (? ?1) means the datum whose number is given in datum number 1. Some tools allow additional slot designations, as shown in the individual descriptions. The second form of template is the ‘named-procedure’ form. If the template is a word rather than a list, it is taken as the name of a procedure. That procedure must accept a number of inputs equal to the number of parallel data slots provided by the tool; the procedure is applied to all of the available data in order. That is, if data ?1 through ?3 are available, the template "PROC is equivalent to [PROC ?1 ?2 ?3]. ? show (map "word [a b c] [d e f]) [ad be cf] ? to dotprod :a :b ; vector dot product op apply "sum (map "product :a :b) end The third form of template is ‘named-slot’ or ‘lambda’ form. This form is indicated by a template list containing more than one member, whose ﬁrst member is itself a list. The ﬁrst member is taken as a list of names; local variables are created with those names and given the available data in order as their values. The number of names must equal the number of available data. This form is needed primarily when one iteration tool must be used within the template list of another, and the ? notation would be ambiguous in the inner template. Example: to matmul :m1 :m2 [:tm2 transpose :m2] ; multiply two matrices output map [[row] map [[col] dotprod :row :col] :tm2] :m1 end The fourth form is ‘procedure text’ form, a variant of lambda form. In this form, the template list contains at least two members, all of which are lists. This is the form used by the DEFINE and TEXT primitives, and APPLY accepts it so that the text of a deﬁned procedure can be used as a template. Note: The fourth form of template is interpreted diﬀerently from the others, in that Logo considers it to be an independent deﬁned procedure for the purposes of OUTPUT and STOP. For example, the following two instructions are identical:

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? print apply [[x] :x+3] [5] 8 ? print apply [[x] [output :x+3]] [5] 8 although the ﬁrst instruction is in named-slot form and the second is in procedure-text form. The named-slot form can be understood as telling Logo to evaluate the expression :x+3 in place of the entire invocation of apply, with the variable x temporarily given the value 5. The procedure-text form can be understood as invoking the procedure to foo :x output :x+3 end with input 5, but without actually giving the procedure a name. If the use of OUTPUT were interchanged in these two examples, we’d get errors: ? print apply [[x] output :x+3] [5] Can only use output inside a procedure ? print apply [[x] [:x+3]] [5] You don’t say what to do with 8 The named-slot form can be used with STOP or OUTPUT inside a procedure, to stop the enclosing procedure. The following iteration tools are extended versions of the ones in Appendix B of the book Computer Science Logo Style, Volume 3: Advanced Topics by Brian Harvey [MIT Press, 1987]. The extensions are primarily to allow for variable numbers of inputs.

apply
APPLY template inputlist command or operation. Runs the template, ﬁlling its slots with the members of inputlist. The number of members in inputlist must be an acceptable number of slots for template. It is illegal to apply the primitive TO as a template, but anything else is okay. APPLY outputs what template outputs, if anything. See [TO], page 49 .

invoke
INVOKE template input (library procedure) (INVOKE template input1 input2 ...) command or operation. Exactly like APPLY except that the inputs are provided as separate expressions rather than in a list.

foreach
FOREACH data template (library procedure) (FOREACH data1 data2 ... template)

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command. Evaluates the template list repeatedly, once for each member of the data list. If more than one data list are given, each of them must be the same length. (The data inputs can be words, in which case the template is evaluated once for each character.) In a template, the symbol ?REST represents the portion of the data input to the right of the member currently being used as the ? slot-ﬁller. That is, if the data input is [A B C D E] and the template is being evaluated with ? replaced by B, then ?REST would be replaced by [C D E]. If multiple parallel slots are used, then (?REST 1) goes with ?1, etc. In a template, the symbol # represents the position in the data input of the member currently being used as the ? slot-ﬁller. That is, if the data input is [A B C D E] and the template is being evaluated with ? replaced by B, then # would be replaced by 2.

map
MAP template data (library procedure) (MAP template data1 data2 ...) outputs a word or list, depending on the type of the data input, of the same length as that data input. (If more than one data input are given, the output is of the same type as data1.) Each member of the output is the result of evaluating the template list, ﬁlling the slots with the corresponding member(s) of the data input(s). (All data inputs must be the same length.) In the case of a word output, the results of the template evaluation must be words, and they are concatenated with WORD. In a template, the symbol ?REST represents the portion of the data input to the right of the member currently being used as the ? slot-ﬁller. That is, if the data input is [A B C D E] and the template is being evaluated with ? replaced by B, then ?REST would be replaced by [C D E]. If multiple parallel slots are used, then (?REST 1) goes with ?1, etc. In a template, the symbol # represents the position in the data input of the member currently being used as the ? slot-ﬁller. That is, if the data input is [A B C D E] and the template is being evaluated with ? replaced by B, then # would be replaced by 2. See [WORD], page 9 .

map.se
MAP.SE template data (library procedure) (MAP.SE template data1 data2 ...) outputs a list formed by evaluating the template list repeatedly and concatenating the results using SENTENCE. That is, the members of the output are the members of the results of the evaluations. The output list might, therefore, be of a diﬀerent length from that of the data input(s). (If the result of an evaluation is the empty list, it contributes nothing to the ﬁnal output.) The data inputs may be words or lists. In a template, the symbol ?REST represents the portion of the data input to the right of the member currently being used as the ? slot-ﬁller. That is, if the data input is [A B C D E] and the template is being evaluated with ? replaced by B, then ?REST would be replaced by [C D E]. If multiple parallel slots are used, then (?REST 1) goes with ?1, etc.

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In a template, the symbol # represents the position in the data input of the member currently being used as the ? slot-ﬁller. That is, if the data input is [A B C D E] and the template is being evaluated with ? replaced by B, then # would be replaced by 2. See [SENTENCE], page 9 .

ﬁlter
FILTER tftemplate data (library procedure) outputs a word or list, depending on the type of the data input, containing a subset of the members (for a list) or characters (for a word) of the input. The template is evaluated once for each member or character of the data, and it must produce a TRUE or FALSE value. If the value is TRUE, then the corresponding input constituent is included in the output. ? print filter "vowelp "elephant eea ? In a template, the symbol ?REST represents the portion of the data input to the right of the member currently being used as the ? slot-ﬁller. That is, if the data input is [A B C D E] and the template is being evaluated with ? replaced by B, then ?REST would be replaced by [C D E]. In a template, the symbol # represents the position in the data input of the member currently being used as the ? slot-ﬁller. That is, if the data input is [A B C D E] and the template is being evaluated with ? replaced by B, then # would be replaced by 2.

ﬁnd
FIND tftemplate data (library procedure) outputs the ﬁrst constituent of the data input (the ﬁrst member of a list, or the ﬁrst character of a word) for which the value produced by evaluating the template with that consituent in its slot is TRUE. If there is no such constituent, the empty list is output. In a template, the symbol ?REST represents the portion of the data input to the right of the member currently being used as the ? slot-ﬁller. That is, if the data input is [A B C D E] and the template is being evaluated with ? replaced by B, then ?REST would be replaced by [C D E]. In a template, the symbol # represents the position in the data input of the member currently being used as the ? slot-ﬁller. That is, if the data input is [A B C D E] and the template is being evaluated with ? replaced by B, then # would be replaced by 2.

reduce
REDUCE template data (library procedure) outputs the result of applying the template to accumulate the members of the data input. The template must be a two-slot function. Typically it is an associative function name like SUM. If the data input has only one constituent (member in a list or character in a word), the output is that consituent. Otherwise, the template is ﬁrst applied with ?1 ﬁlled with the next-to-last consitient and ?2 with the last constituent. Then, if there are more

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constituents, the template is applied with ?1 ﬁlled with the next constituent to the left and ?2 with the result from the previous evaluation. This process continues until all constituents have been used. The data input may not be empty. Note: If the template is, like SUM, the name of a procedure that is capable of accepting arbitrarily many inputs, it is more eﬃcient to use APPLY instead of REDUCE. The latter is good for associative procedures that have been written to accept exactly two inputs: to max :a :b output ifelse :a > :b [:a] [:b] end print reduce "max [...] Alternatively, REDUCE can be used to write MAX as a procedure that accepts any number of inputs, as SUM does: to max [:inputs] 2 if emptyp :inputs ~ [(throw "error [not enough inputs to max])] output reduce [ifelse ?1 > ?2 [?1] [?2]] :inputs end See [SUM], page 29 , [APPLY], page 76 .

crossmap
CROSSMAP template listlist (library procedure) (CROSSMAP template data1 data2 ...) outputs a list containing the results of template evaluations. Each data list contributes to a slot in the template; the number of slots is equal to the number of data list inputs. As a special case, if only one data list input is given, that list is taken as a list of data lists, and each of its members contributes values to a slot. CROSSMAP diﬀers from MAP in that instead of taking members from the data inputs in parallel, it takes all possible combinations of members of data inputs, which need not be the same length. ? show (crossmap [word ?1 ?2] [a b c] [1 2 3 4]) [a1 a2 a3 a4 b1 b2 b3 b4 c1 c2 c3 c4] ? For compatibility with the version in the ﬁrst edition of CSLS1, CROSSMAP templates may use the notation :1 instead of ?1 to indicate slots. See [MAP], page 77 .

cascade
CASCADE endtest template startvalue (library procedure) (CASCADE endtest tmp1 sv1 tmp2 sv2 ...) (CASCADE endtest tmp1 sv1 tmp2 sv2 ... finaltemplate)
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outputs the result of applying a template (or several templates, as explained below) repeatedly, with a given value ﬁlling the slot the ﬁrst time, and the result of each application ﬁlling the slot for the following application. In the simplest case, CASCADE has three inputs. The second input is a one-slot expression template. That template is evaluated some number of times (perhaps zero). On the ﬁrst evaluation, the slot is ﬁlled with the third input; on subsequent evaluations, the slot is ﬁlled with the result of the previous evaluation. The number of evaluations is determined by the ﬁrst input. This can be either a nonnegative integer, in which case the template is evaluated that many times, or a predicate expression template, in which case it is evaluated (with the same slot ﬁller that will be used for the evaluation of the second input) repeatedly, and the CASCADE evaluation continues as long as the predicate value is FALSE. (In other words, the predicate template indicates the condition for stopping.) If the template is evaluated zero times, the output from CASCADE is the third (startvalue) input. Otherwise, the output is the value produced by the last template evaluation. CASCADE templates may include the symbol # to represent the number of times the template has been evaluated. This slot is ﬁlled with 1 for the ﬁrst evaluation, 2 for the second, and so on. ? show [1 2 3 ? show ing ? show 120 ? cascade 5 [lput # ?] [] 4 5] cascade [vowelp first ?] [bf ?] "spring cascade 5 [# * ?] 1

Several cascaded results can be computed in parallel by providing additional templatestartvalue pairs as inputs to CASCADE. In this case, all templates (including the endtest template, if used) are multi-slot, with the number of slots equal to the number of pairs of inputs. In each round of evaluations, ?2, for example, represents the result of evaluating the second template in the previous round. If the total number of inputs (including the ﬁrst endtest input) is odd, then the output from CASCADE is the ﬁnal value of the ﬁrst template. If the total number of inputs is even, then the last input is a template that is evaluated once, after the end test is satisﬁed, to determine the output from CASCADE. to fibonacci :n output (cascade :n [?1 + ?2] 1 [?1] 0) end to piglatin :word output (cascade [vowelp first ?] ~ [word bf ? first ?] ~ :word ~ [word ? "ay]) end

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cascade.2
CASCADE.2 endtest temp1 startval1 temp2 startval2 (library procedure) outputs the result of invoking CASCADE with the same inputs. The only diﬀerence is that the default number of inputs is ﬁve instead of three.

transfer
TRANSFER endtest template inbasket (library procedure) outputs the result of repeated evaluation of the template. The template is evaluated once for each member of the list inbasket. TRANSFER maintains an outbasket that is initially the empty list. After each evaluation of the template, the resulting value becomes the new outbasket. In the template, the symbol ?IN represents the current member from the inbasket; the symbol ?OUT represents the entire current outbasket. Other slot symbols should not be used. If the ﬁrst (endtest) input is an empty list, evaluation continues until all inbasket members have been used. If not, the ﬁrst input must be a predicate expression template, and evaluation continues until either that template’s value is TRUE or the inbasket is used up.

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9 Macros
.macro
.MACRO procname :input1 :input2 ... .DEFMACRO procname text (special form)

A macro is a special kind of procedure whose output is evaluated as Logo instructions in the context of the macro’s caller. .MACRO is exactly like TO except that the new procedure becomes a macro; .DEFMACRO is exactly like DEFINE with the same exception. Macros are useful for inventing new control structures comparable to REPEAT, IF, and so on. Such control structures can almost, but not quite, be duplicated by ordinary Logo procedures. For example, here is an ordinary procedure version of REPEAT: to my.repeat :num :instructions if :num=0 [stop] run :instructions my.repeat :num-1 :instructions end This version works ﬁne for most purposes, e.g., my.repeat 5 [print "hello] But it doesn’t work if the instructions to be carried out include OUTPUT, STOP, or LOCAL. For example, consider this procedure: to example print [Guess my secret word. You get three guesses.] repeat 3 [type "|?? | ~ if readword = "secret [pr "Right! stop]] print [Sorry, the word was "secret"!] end This procedure works as written, but if MY.REPEAT is used instead of REPEAT, it won’t work because the STOP will stop MY.REPEAT instead of stopping EXAMPLE as desired. The solution is to make MY.REPEAT a macro. Instead of actually carrying out the computation, a macro must return a list containing Logo instructions. The contents of that list are evaluated as if they appeared in place of the call to the macro. Here’s a macro version of REPEAT: .macro my.repeat :num :instructions if :num=0 [output []] output sentence :instructions ~ (list "my.repeat :num-1 :instructions) end Every macro is an operation — it must always output something. Even in the base case, MY.REPEAT outputs an empty instruction list. To show how MY.REPEAT works, let’s take the example

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my.repeat 5 [print "hello] For this example, MY.REPEAT will output the instruction list [print "hello my.repeat 4 [print "hello]] Logo then executes these instructions in place of the original invocation of MY.REPEAT; this prints hello once and invokes another repetition. The technique just shown, although fairly easy to understand, has the defect of slowness because each repetition has to construct an instruction list for evaluation. Another approach is to make MY.REPEAT a macro that works just like the non-macro version unless the instructions to be repeated include OUTPUT or STOP: .macro my.repeat :num :instructions catch "repeat.catchtag ~ [op repeat.done runresult [repeat1 :num :instructions]] op [] end to repeat1 :num :instructions if :num=0 [throw "repeat.catchtag] run :instructions .maybeoutput repeat1 :num-1 :instructions end to repeat.done :repeat.result if emptyp :repeat.result [op [stop]] op list "output quoted first :repeat.result end If the instructions do not include STOP or OUTPUT, then REPEAT1 will reach its base case and invoke THROW. As a result, MY.REPEAT’s last instruction line will output an empty list, so the evaluation of the macro result by the caller will do nothing. But if a STOP or OUTPUT happens, then REPEAT.DONE will output a STOP or OUTPUT instruction that will be executed in the caller’s context. The macro-deﬁning commands have names starting with a dot because macros are an advanced feature of Logo; it’s easy to get in trouble by deﬁning a macro that doesn’t terminate, or by failing to construct the instruction list properly. Lisp users should note that Logo macros are not special forms. That is, the inputs to the macro are evaluated normally, as they would be for any other Logo procedure. It’s only the output from the macro that’s handled unusually. Here’s another example: .macro localmake :name :value output (list "local ~ word "" :name ~ "apply ~

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""make ~ (list :name :value)) end It’s used this way: to try localmake "garply "hello print :garply end LOCALMAKE outputs the list [local "garply apply "make [garply hello]] The reason for the use of APPLY is to avoid having to decide whether or not the second input to MAKE requires a quotation mark before it. (In this case it would — MAKE "GARPLY "HELLO — but the quotation mark would be wrong if the value were a list.) It’s often convenient to use the ‘ function to construct the instruction list: .macro localmake :name :value op ‘[local ,[word "" :name] apply "make [,[:name] ,[:value]]] end On the other hand, ‘ is pretty slow, since it’s tree recursive and written in Logo. See [TO], page 49 , [DEFINE], page 50 , [APPLY], page 76 , [STOP], page 69 , [OUTPUT], page 69 .

.defmacro
See [dMACRO], page 83 .

macrop
MACROP name MACRO? name outputs TRUE if its input is the name of a macro.

macroexpand
MACROEXPAND expr (library procedure) takes as its input a Logo expression that invokes a macro (that is, one that begins with the name of a macro) and outputs the the Logo expression into which the macro would translate the input expression. .macro localmake :name :value op ‘[local ,[word "" :name] apply "make [,[:name] ,[:value]]] end ? show macroexpand [localmake "pi 3.14159] [local "pi apply "make [pi 3.14159]]

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10 Error Processing
If an error occurs, Logo takes the following steps. First, if there is an available variable named ERRACT, Logo takes its value as an instructionlist and runs the instructions. The operation ERROR may be used within the instructions (once) to examine the error condition. If the instructionlist invokes PAUSE, the error message is printed before the pause happens. Certain errors are recoverable; for one of those errors, if the instructionlist outputs a value, that value is used in place of the expression that caused the error. (If ERRACT invokes PAUSE and the user then invokes CONTINUE with an input, that input becomes the output from PAUSE and therefore the output from the ERRACT instructionlist.) It is possible for an ERRACT instructionlist to produce an inappropriate value or no value where one is needed. As a result, the same error condition could recur forever because of this mechanism. To avoid that danger, if the same error condition occurs twice in a row from an ERRACT instructionlist without user interaction, the message ‘Erract loop’ is printed and control returns to toplevel. "Without user interaction" means that if ERRACT invokes PAUSE and the user provides an incorrect value, this loop prevention mechanism does not take eﬀect and the user gets to try again. During the running of the ERRACT instructionlist, ERRACT is locally unbound, so an error in the ERRACT instructions themselves will not cause a loop. In particular, an error during a pause will not cause a pause-within-a-pause unless the user reassigns the value [PAUSE] to ERRACT during the pause. But such an error will not return to toplevel; it will remain within the original pause loop. If there is no available ERRACT value, Logo handles the error by generating an internal THROW "ERROR. (A user program can also generate an error condition deliberately by invoking THROW.) If this throw is not caught by a CATCH "ERROR in the user program, it is eventually caught either by the toplevel instruction loop or by a pause loop, which prints the error message. An invocation of CATCH "ERROR in a user program locally unbinds ERRACT, so the eﬀect is that whichever of ERRACT and CATCH "ERROR is more local will take precedence. If a ﬂoating point overﬂow occurs during an arithmetic operation, or a two-input mathematical function (like POWER) is invoked with an illegal combination of inputs, the ‘doesn’t like’ message refers to the second operand, but should be taken as meaning the combination. See [ERRACT], page 89 , [THROW], page 69 , [ERROR], page 70 , [CATCH], page 69 , [PAUSE], page 70 , [CONTINUE], page 70 .

10.1 Error Codes
Here are the numeric codes that appear as the ﬁrst member of the list output by ERROR when an error is caught, with the corresponding messages. Some messages may have two diﬀerent codes depending on whether or not the error is recoverable (that is, a substitute value can be provided through the ERRACT mechanism) in the speciﬁc context. Some messages are warnings rather than errors; these will not be caught. Errors 0 and 32 are so bad that Logo exits immediately. 0 Fatal internal error (can’t be caught)

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Out of memory Stack overflow Turtle out of bounds proc doesn’t like datum as input (not recoverable) proc didn’t output to proc Not enough inputs to proc proc doesn’t like datum as input (recoverable) Too much inside ()’s You don’t say what to do with datum ’)’ not found var has no value Unexpected ’)’ I don’t know how to proc (recoverable) Can’t find catch tag for throwtag proc is already defined Stopped Already dribbling File system error Assuming you mean IFELSE, not IF (warning only) var shadowed by local in procedure call (warning only) Throw "Error proc is a primitive Can’t use TO inside a procedure I don’t know how to proc (not recoverable) IFTRUE/IFFALSE without TEST Unexpected ’]’ Unexpected ’}’ Couldn’t initialize graphics Macro returned value instead of a list You don’t say what to do with value Can only use STOP or OUTPUT inside a procedure APPLY doesn’t like badthing as input END inside multi-line instruction Really out of memory (can’t be caught) user-generated error message (THROW "ERROR message ) END inside multi-line instruction Bad default expression for optional input: expr Can’t use OUTPUT or STOP inside RUNRESULT Assuming you meant ’FD 100’, not FD100 (or similar) I can’t open file filename File filename already open File filename not open Runlist [expr expr ] has more than one expression.

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11 Special Variables
Logo takes special action if any of the following variable names exists. They follow the normal scoping rules, so a procedure can locally set one of them to limit the scope of its eﬀect. Initially, no variables exist except for ALLOWGETSET, CASEIGNOREDP, and UNBURYONEDIT, which are TRUE and buried.

allowgetset
ALLOWGETSET (variable) if TRUE, indicates that an attempt to use a procedure that doesn’t exist should be taken as an implicit getter or setter procedure (setter if the ﬁrst three letters of the name are SET) for a variable of the same name (without the SET if appropriate).

buttonact
BUTTONACT (variable) if nonempty, should be an instruction list that will be evaluated whenever a mouse button is pressed. Note that the user may have released the button before the instructions are evaluated. BUTTON will still output which button was most recently pressed. CLICKPOS will output the position of the mouse cursor at the moment the button was pressed; this may be diﬀerent from MOUSEPOS if the user moves the mouse after clicking. Note that it’s possible for the user to press a button during the evaluation of the instruction list. If this would confuse your program, prevent it by temporarily setting BUTTONACT to the empty list. One easy way to do that is the following: make "buttonact [button.action] to button.action [:buttonact []] ... ; whatever you want the button to do end

caseignoredp
CASEIGNOREDP (variable) if TRUE, indicates that lower case and upper case letters should be considered equal by EQUALP, BEFOREP, MEMBERP, etc. Logo initially makes this variable TRUE, and buries it. See [EQUALP], page 14 , [BEFOREP], page 15 , [MEMBERP], page 15 .

commandline
COMMANDLINE (variable) contains any text appearing after a hyphen on the command line used to start Logo.

erract
ERRACT (variable)

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an instructionlist that will be run in the event of an error. Typically has the value [PAUSE] to allow interactive debugging. See [PAUSE], page 70 .

fullprintp
FULLPRINTP (variable) if TRUE, then words that were created using backslash or vertical bar (to include characters that would otherwise not be treated as part of a word) are printed with the backslashes or vertical bars shown, so that the printed result could be re-read by Logo to produce the same value. If FULLPRINTP is TRUE then the empty word (however it was created) prints as ||. (Otherwise it prints as nothing at all.)

keyact
KEYACT (variable) if nonempty, should be an instruction list that will be evaluated whenever a key is pressed on the keyboard. The instruction list can use READCHAR to ﬁnd out what key was pressed. Note that only keys that produce characters qualify; pressing SHIFT or CONTROL alone will not cause KEYACT to be evaluated. Note that it’s possible for the user to press a key during the evaluation of the instruction list. If this would confuse your program, prevent it by temporarily setting KEYACT to the empty list. One easy way to do that is the following: make "keyact [key.action] to key.action [:keyact []] ... ; whatever you want the key to do end

loadnoisily
LOADNOISILY (variable) if TRUE, prints the names of procedures deﬁned when loading from a ﬁle (including the temporary ﬁle made by EDIT). See [EDIT], page 61 .

printdepthlimit
PRINTDEPTHLIMIT (variable) if a nonnegative integer, indicates the maximum depth of sublist structure that will be printed by PRINT, etc. See [PRINT], page 19 .

printwidthlimit
PRINTWIDTHLIMIT (variable)

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if a nonnegative integer, indicates the maximum number of members in any one list that will be printed by PRINT, etc. See [PRINT], page 19 .

redefp
REDEFP (variable) if TRUE, allows primitives to be erased (ERASE) or redeﬁned (COPYDEF). See [ERASE], page 57 , [COPYDEF], page 51 .

startup
STARTUP (variable) if assigned a list value in a ﬁle loaded by LOAD, that value is run as an instructionlist after the loading. See [LOAD], page 63 .

unburyonedit
UNBURYONEDIT (variable) if TRUE, causes any procedure deﬁned during EDIT or LOAD to be unburied, so that it will be saved by a later SAVE. Files that want to deﬁne and bury procedures must do it in that order. See [EDIT], page 61 , See [LOAD], page 63 , See [SAVE], page 62 .

usealternatenames
USEALTERNATENAMES (variable) if TRUE, causes Logo to generate non-English words (from the ‘Messages’ ﬁle) instead of TRUE, FALSE, END, etc. Logo provides the following buried variables that can be used by programs:

logoversion
LOGOVERSION a real number indicating the Logo version number, e.g., 5.5 (variable)

logoplatform
LOGOPLATFORM (variable) one of the following words: wxWidgets, X11, Windows, or Unix-nographics.

Chapter 12: Internationalization

93

12 Internationalization
Berkeley Logo has limited support for non-English-speaking users. Alas, there is no Unicode support, and high-bit-on ASCII codes work in some contexts but not others. If you want to translate Berkeley Logo for use with another language, there are three main things you have to do: 1. Primitive names 2. Error (and other) messages 3. Documentation For primitive names, the easiest thing is to provide a startup ﬁle that deﬁnes aliases for the English primitive names, using COPYDEF: COPYDEF "AVANT "FORWARD This should take care of it, unless your language’s name for one primitive is spelled like the English name of a diﬀerent primitive. In that case you have to turn REDEFP on and be sure to copy the non-conﬂicting name before overwriting the conﬂicting one! "Primitives" that are actually in the Logo library, of course, can just be replaced or augmented with native-language-named Logo procedures and ﬁlenames. Of course Logo programs will still not look like your native language if the word order is dramatically diﬀerent, especially if you don’t put verbs before their objects. For error messages, there is a ﬁle named ‘Messages’ in the ‘logolib’ directory with texts of messages, one per line. You can replace this with a ﬁle for your own language. Do not add, delete, or reorder lines; Logo ﬁnds messages by line number. The sequences %p, %s, and %t in these messages represent variable parts of the message and should not be translated. (%p PRINTs the variable part, while %s SHOWs it – that is, the diﬀerence is about whether or not brackets are shown surrounding a list. %t means that the variable part is a C text string rather than a Logo object.) If you want to change the order of two variable parts (no reorderable message has more than two), you would for example replace the line %p doesn’t like %s as input with %+s is a lousy input to %p The plus sign tells the message printer to reverse the order; you must reverse the order of %p and %s, if both are used, to match. The plus sign goes just after the ﬁrst percent sign in the message, which might not be at the beginning of the line. The sequence \n in a message represents a newline; don’t be fooled into thinking that the n is part of the following word. Some messages appear twice in the ﬁle; this isn’t a mistake. The two spaces before to in I don’t know how\ \ to aren’t a mistake either. The message containing just %p is for user-provided error messages in THROW "ERROR. The message "\ \ in %s\n%s" is the part of all error messages that indicates where the error occurred if it was inside a procedure; you might want to change the word in to your language. %s defined\n is what LOAD prints

94

BERKELEY LOGO 6.0

for each procedure deﬁned if the variable LOADNOISILY is TRUE. "to %p\nend\n\n" is what EDIT puts in the temporary ﬁle if you ask to edit a procedure that isn’t already deﬁned. Also in the ‘Messages’ ﬁle are lines containing only one word each; the ﬁrst of these is the word true. Some of these words are recognized by Logo in user input; some are generated by Logo; some are both. For example, the words TRUE and FALSE are recognized as Boolean values by IF and IFELSE, and are also generated by Logo as outputs from the primitive predicates such as EQUALP. The word END is recognized as the end of a procedure deﬁnition, and may be generated when Logo reconstructs a procedure body for PO or EDIT. I’ve used capital letters in this paragraph for easier reading, but the words in the ‘Messages’ ﬁle should be in lower case. If you replace these with non-English words, Logo will recognize both the English names and your alternate names. For example, if you replace the word true with vrai then Logo will understand both of these: IF "TRUE [PRINT "YES] IF "VRAI [PRINT "YES] The variable UseAlternateNames determines whether Logo will generate other-language names – for example, whether predicate functions return the other-language alternates for TRUE and FALSE. This variable is FALSE by default, meaning that the English words will be generated. You might wish to have English-named predicate functions generate English TRUE and FALSE, while other-language-named predicates generate the alternate words. This can be done by leaving UseAlternateNames false, and instead of deﬁning the other-language predicates with COPYDEF, do it this way: to french.boolean :bool if equalp :bool "true [output "vrai] if equalp :bool "false [output "faux] output :bool ; shouldn’t happen end to make.french.predicate :french :english :arity define :french ‘[[[inputs] ,[:arity]] [output french.boolean apply ,[word "" :english] :inputs]] end ? make.french.predicate "egal? "equal? 2 ? pr egal? 3 4 faux ? pr egal? 4 4 vrai ? pr equal? 3 4 false ? pr equal? 4 4

Chapter 12: Internationalization

95

true The third input to make.french.predicate is the number of inputs that the predicate expects. This solution isn’t quite perfect because the inﬁx predicates (=, <, >) will still output in English. If you want them to generate alternate-language words, set UseAlternateNames to TRUE instead. Some of the words in this section of the ‘Messages’ ﬁle are names of Logo primitives (OUTPUT, STOP, GOTO, TAG, IF, IFELSE, TO, .MACRO). To translate these names, you must use COPYDEF as described earlier, in addition to changing the names in ‘Messages’. You should be consistent in these two steps. Don’t forget the period in .macro! For documentation, there are two kinds: this manual and the help ﬁles. The latter are generated automatically from this manual if you have a Unix system, so in that case you need only translate this manual, maintaining the format. (The automatic helpﬁle generator notices things like capital letters, tabs, hyphens, and equal signs at the beginnings of lines.) The program makefile.c may require modiﬁcation because a few of the primitive names are special cases (e.g., LOG10 is the only name with digits included). If you don’t have Unix tools, you can just translate each helpﬁle individually. A period in a primitive name is represented as a D in the ﬁlename; there are no ﬁles for question marks because the HELP command looks for the ﬁle named after the corresponding primitive that ends in P.

INDEX

97

INDEX
*
* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 arity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 array? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 arrayp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 arraytolist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ascii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 ashift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

+
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

B
back . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . before? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . beforep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bfs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bitand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bitnot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bitxor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buried . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buried? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buriedp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buryall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buryname . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . butﬁrst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . butﬁrsts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . butlast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . button . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . button? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buttonact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . buttonp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bye . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 46 15 15 11 11 46 33 34 33 33 37 12 54 60 60 59 59 59 11 11 12 47 47 89 47 71

.
.defmacro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .eq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .maybeoutput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .setbf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .setﬁrst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .setitem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .setsegmentsize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 15 83 71 13 13 13 65

/
/ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

<
< . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 <= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 <> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

=
= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

>
> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 >= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

C
cascade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 cascade.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 case-insensitive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 caseignoredp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 catch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 char . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 clean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 clearscreen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 cleartext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 clickpos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 close . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 closeall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 co . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 combine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

‘
‘ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

A
allopen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 allowgetset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 AllowGetSet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 apply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 arc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 arctan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

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BERKELEY LOGO 6.0

commandline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Computer Science Logo Style. . . . . . . . . . . . . . . . . . . 1 cond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 continue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 copydef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Copyright . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 cos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 crossmap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 cs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 cslsload. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 ct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 cursor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

erract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . exp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

89 70 87 30

F
fd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 fence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 ﬁle? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 ﬁlep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 ﬁll. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 ﬁlled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 ﬁlter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 ﬁnd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 ﬁrst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ﬁrsts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 for . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 foreach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 forever . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 forward. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 fput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 fs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 fullprintp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 fullscreen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 fulltext . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

D
decreasefont . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 deﬁne . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 deﬁned? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 deﬁnedp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 delimiters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 dequeue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 diﬀerence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 do.until . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 do.while . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 dribble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

E
ed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . editﬁle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . editor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edpl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edpls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . edps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . empty? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . emptyp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . eof? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . eofp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . epspict . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . equal? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . equalp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . er . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . eraseﬁle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erpl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erpls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . erps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 62 61 61 61 62 62 62 62 62 14 14 25 25 47 14 14 57 58 57 23 23 58 58 58 58 58

G
gc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 gensym . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 getter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 global . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 goto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 gprop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 greater? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 greaterequal? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 greaterequalp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 greaterp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

H
heading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . hideturtle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . home . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ht . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 63 40 38 40

I
if . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ifelse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iﬀ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iﬀalse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iftrue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 68 68 68 68 68

INDEX

99

ignore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . increasefont . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . int . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . invoke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iseq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . item . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

72 27 30 76 31 12

minus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 modulo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 mousepos. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

N
name . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . name? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . namelist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . namep. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . nodribble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . norefresh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . not . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . notequal?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . notequalp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . number?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . numberp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 54 55 54 55 56 24 42 35 15 15 16 16

K
key? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 keyact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 keyp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

L
label . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 labelsize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 last. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 leaving ucblogo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 left . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 less?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 lessequal? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 lessequalp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 lessp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 line-continuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 list? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 listp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 listtoarray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ln . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 loadnoisily . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 loadpict . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 local . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 localmake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 log10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 logohelp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 logoplatform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 logoversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 lowercase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 lput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 lshift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 lt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

O
op . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . openappend . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . openread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . openupdate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . openwrite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . or . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 23 22 23 22 35 69

P
palette . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . parse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pause. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pencolor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pendown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pendown? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pendownp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . penerase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . penmode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . penpaint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . penpattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . penreverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pensize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . penup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . plist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . plist? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . plistp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . plists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pllist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . po . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . poall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 18 70 45 43 44 46 45 43 45 45 44 45 44 46 44 46 43 12 53 54 54 55 55 56 56

M
macro? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . macroexpand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . macrop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . make . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . map.se . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . mdarray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . mditem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . mdsetitem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . member? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . memberp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 85 85 51 77 77 10 12 13 17 15 15

100

BERKELEY LOGO 6.0

pon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . popl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . popls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pprop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ppt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . preﬁx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . primitive? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . primitivep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . print . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . printdepthlimit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . printout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . printwidthlimit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . procedure? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . procedurep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . product . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pu. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . push . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . px . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

57 56 13 57 57 56 39 57 57 30 53 44 19 22 53 53 55 19 90 56 90 53 53 55 29 43 13 44

repcount . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 repeat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 rerandom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 reverse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 right . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 rl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 round . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 rseq . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 rt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 run . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 runparse. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 runparsing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 runresult . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 rw. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

S
save . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 savel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 savepict . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 screenmode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 scrunch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 scrunch.dat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 se . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 sentence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 setbackground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 setbg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 setcslsloc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 setcursor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 seteditor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 setfont . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 seth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 setheading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 sethelploc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 setitem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 setlabelheight. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 setlibloc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 setmargins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 setpalette. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 setpc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 setpen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 setpencolor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 setpenpattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 setpensize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 setpos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 setpreﬁx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 setread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 setreadpos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 setscrunch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 settc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 settemploc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 setter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 settextcolor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 settextsize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 setwrite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 setwritepos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 setx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 setxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Q
queue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 quoted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 quotient . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

R
radarctan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . radcos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . radsin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . random. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . rawascii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . rc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . rcs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . readchar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . readchars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . reader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . readlist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . readpos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . readrawline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . readword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . redefp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . reduce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . refresh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . remainder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . remdup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . remove . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . remprop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 31 31 32 16 21 21 21 21 25 20 25 20 20 91 78 42 30 12 12 53

INDEX

101

sety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 show . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 shown? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 shownp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 showturtle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 sin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 splitscreen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 sqrt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 ss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 st . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 standout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 starting ucblogo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 stepped . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 stepped? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 steppedp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 substring? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 substringp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 sum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 turtlemode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

U
unbury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . unburyall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . unburyname . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . unburyonedit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . unstep. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . until . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . untrace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . uppercase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . usealternatenames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 59 59 91 60 73 60 17 91

V
vbarred? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 vbarredp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

T
tag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . temp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . template . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . textscreen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . textsize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . thing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . throw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . to . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . towards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . trace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . traced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . traced? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . tracedp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 61 74 68 51 41 27 52 69 49 39 60 54 60 60

W
wait . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 while . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 wordp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 wrap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 writepos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 writer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

X
xcor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Y
ycor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

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