Exemple de primitives logo imlémentées

  - https://turing.cs.hbg.psu.edu/LOCAL/ucblogo/ucbl_7.htm   - https://fmslogo.sourceforge.io/manual/workspace-control.html   - https://www.calormen.com/jslogo/language.html 
 
 
 The section numbers are per the Berkeley Logo Reference Manual in Brian Harvey's Computer Science Logo Style volume 2: Advanced Techniques for ease of comparison. 
 
 
 Data Types and Syntax 
 Data Structure Primitives 
 Communication 
 Arithmetic 
 Logical Operations 
 Graphics 
 Workspace Management 
 Control Structures 
 
 
 Data Types and Syntax 
 
 
 " word 
 ' word 
 number 
 Word. (Quoted words are terminated by [](){} or whitespace, \ to escape.) 
 show "hello 
 show "hello\ logo 
 show 12.34 
 : variable 
 Input definition/variable reference 
 show :name 
 [ word ... ] 
 List of words or lists, whitespace separated 
 show [1 2 3] 
 { word ... } 
 { word ... }@ origin 
 Array of words, whitespace separated 
 show {1 2 3} 
 ( expression ) 
 Parenthesis can be used to group expressions 
 show ( 1 + 2 ) * 3 
 procedure input ... 
 Call procedure with default number of inputs 
 show "hello 
 ( procedure input ... ) 
 Call procedure with an arbitrary number of inputs 
 (show "hello :name) 
 
 
 2. Data Structure Primitives 
 2.1 Constructors 
 
 
 word expr expr 
 (word expr ... ) 
 Concatenate two (or more) words into one word 
 show (word "a "b "c) 
 list thing1 thing2 
 (list thing1 thing2 ...) 
 Create a new list from the inputs 
 show (list 1+2 2+3 3+4) 
 sentence thing1 thing2 
 (sentence thing1 thing2 ...) 
 se thing1 thing2 
 (se thing1 thing2 ...) 
 Create a new list from the inputs (if non-lists) or members of the inputs (if lists) 
 show sentence [1 2 3] [and so on] 
 fput thing list 
 lput thing list 
 Outputs list, but with thing added as a new first/last item; if list is a word, concatenates 
 show fput 0 [ 1 2 3 ] 
 show fput "a "bcd 
 show lput 4 [ 1 2 3 ] 
 show lput "e "bcd 
 array size 
 (array size origin ) 
 Create a new array. The default origin is 1. 
 show array 10 
 mdarray [ dimensions ...] 
 (mdarray [ dimensions ...] origin ) 
 Create a new multi-dimensional array. The default origin is 1. 
 show mdarray [2 2] 
 listtoarray list 
 (listtoarray list origin ) 
 Create a new array populated by members of a list 
 show listtoarray [ 1 3 5 7 ] 
 arraytolist array 
 Create a new list populated by members of a array 
 show arraytolist { 2 4 6 8 } 
 combine thing1 thing2 
 If thing2 is a word, like word ; otherwise, like fput 
 show combine "a [b c] 
 reverse list 
 Outputs a list with the items in reverse order; if input is a word, reverses characters 
 show reverse [ 1 2 3 ] 
 show reverse "abc 
 gensym 
 Outputs a unique string, e.g. G1 , G2 , etc. 
 show gensym 
 
 
 2.2 Data Selectors 
 
 
 first list 
 last list 
 Outputs the first or last item (or character) from the list (or word), respectively 
 show first [ 1 2 3 ] 
 show first "abc 
 show last [ 1 2 3 ] 
 show last "abc 
 firsts listoflists 
 Outputs a list of the first item (or character) of each sublist (or word) 
 show firsts [ [1 2 3] [a b c] ] 
 show firsts [ abc def ] 
 butfirst list 
 bf list 
 butlast list 
 bl list 
 Outputs the list (or word), except for the first/last item (or character) 
 show butfirst [ 1 2 3 ] 
 show butfirst "abc 
 show butlast [ 1 2 3 ] 
 show butlast "abc 
 butfirsts listoflists 
 bfs listoflists 
 Outputs a list of sublists (or words) without the first item (or characters) 
 show butfirsts [ [ 1 2 3 ] [ a b c ] ] 
 show butfirsts [ abc def ] 
 item index thing 
 Outputs the indexth item of the list or array or word 
 show item 2 [ 1 2 3 ] 
 show item 2 "abc 
 mditem [ index ...] thing 
 Outputs an item from a multi-dimensional array 
 show mditem [2 1] {{a b} {c d}} 
 pick list 
 Outputs one item from a list (or word), at random 
 show pick [ 1 2 3 ] 
 show pick "abc 
 remove thing list 
 Outputs the list (or word) with any occurences of thing removed 
 show remove "b [ a b c ] 
 show remove "a "banana 
 remdup list 
 Outputs the list (or word) with duplicates removed 
 show remdup [ 1 2 3 2 3 4 3 4 5 ] 
 show remdup "banana 
 quoted thing 
 Outputs thing with " prepended if a word, or just thing otherwise. 
 show quoted "abc 
 split thing list 
 Outputs the list split into a list of lists (or list of words) wherever thing appears. 
 show split "a "banana 
 show split 3 [1 2 3 4 1 2 3 4] 
 
 
 2.3 Data Mutators 
 
 
 setitem index array value 
 Sets the indexth item of the array to value (circular arrays prevented) 
 make "a { 1 2 3 } setitem 2 :a "x show :a 
 mdsetitem [ index ...] array value 
 Sets an item in a multi-dimensional array to value (circular arrays prevented) 
 make "a {{1 2} {3 4}} mdsetitem [2 1] :a "x show :a 
 .setfirst list value 
 Sets the first item of the list to value 
 make "a [ 1 2 3 ] .setfirst :a "7 show :a 
 .setbf list value 
 Sets the 'butfirst' of the list to the items in value (a list) 
 make "a [ 1 2 3 ] .setbf :a [ 4 9 ] show :a 
 .setitem index array value 
 Sets the indexth item of the array to value (circular arrays allowed) 
 make "a { 1 2 3 } setitem 2 :a "x show :a 
 push stackname thing 
 pop stackname 
 Push to/pop from a stack i.e. list variable. Stacks grow from the front. Works on words. 
 make "s [ 2 1 ] push "s 3 show :s show pop "s 
 make "s "ba push "s "c show :s show pop "s 
 queue stackname thing 
 dequeue stackname 
 Add/remove from a queue i.e. list variable, Queues grow from the end. Works on words. 
 make "q [ 1 2 ] queue "q 3 show :q show dequeue "q 
 make "q "ab queue "q "c show :q show dequeue "q 
 
 
 2.4 Predicates 
 Predicates return 1 (true) or 0 (false) 
 
 
 wordp thing 
 word? thing 
 listp thing 
 list? thing 
 arrayp thing 
 array? thing 
 numberp thing 
 number? thing 
 Test if thing is a word, list, array, or number respectively. 
 emptyp expr 
 empty? expr 
 Test if thing is an empty list or empty string. 
 equalp expr expr 
 equal? expr expr 
 expr = expr 
 notequalp expr expr 
 notequal? expr expr 
 expr <> expr 
 Equality/inequality tests. Compares strings, numbers, or lists (equal if length and all members are equal). 
 beforep thing1 thing2 
 before? thing1 thing2 
 Test string collation order. 
 .eq thing1 thing2 
 Test if things have the same identity. 
 memberp thing list 
 member? thing list 
 Test if thing is equal to any member of list. 
 substringp thing1 thing2 
 substring? thing1 thing2 
 Test if thing1 is a substring of thing2. 
 
 
 2.5 Queries 
 
 
 count thing 
 Outputs length of a list or number of characters in a string 
 show count [ 1 2 3 ] 
 show count "hello 
 ascii expr 
 Outputs ASCII (actually, Unicode) code point for first character of string 
 show ascii "abc 
 char expr 
 Outputs Unicode character at specified code point 
 show char 97 
 member thing list 
 Outputs the list (or word) from the first occurence of thing to the end, or empty list (or word) 
 show member "a "banana 
 show member 2 [1 2 3 4] 
 uppercase expr 
 lowercase expr 
 Outputs string converted to upper/lowercase 
 show uppercase "abc 
 show lowercase "ABC 
 standout expr 
 Outputs string with alphanumeric characters in bold 
 show standout "ABCabc123 
 parse word 
 Outputs word parsed as a list. 
 show parse "1+2 
 runparse word 
 Outputs word parsed as instructions. 
 show runparse "1+2 
 
 
 3. Communication 
 3.1 Transmitters 
 
 
 print thing 
 pr thing 
 ( print thing1 thing2 ...) 
 ( pr thing1 thing2 ...) 
 Print inputs to the text screen, separated by spaces, and followed by a newline. Square brackets are only put around sublists. 
 print "hello 
 type thing 
 ( type thing1 thing2 ...) 
 Like print but with no trailing newline. 
 type "hel type "lo 
 show thing 
 ( show thing1 thing2 ...) 
 Like print but with square brackets around list inputs. 
 show "hello 
 
 
 3.2 Receivers 
 
 
 readlist 
 (readlist promptstr ) 
 Prompt the user for a line of input. The result is a list of words. 
 show readlist 
 make "colors (readlist [Type some colors:]) show :colors 
 readword 
 (readword promptstr ) 
 Prompt the user for a line of input. The result (including spaces) is the single word output. 
 show readword 
 make "name (readword [What is your name?]) show :name 
 
 
 3.4 Terminal Access 
 
 
 cleartext 
 ct 
 Clear the text screen. 
 settextcolor color 
 Change the text color. 
 textcolor 
 Output the current text color. 
 increasefont 
 decreasefont 
 Increase/decrease the text size. 
 settextsize height 
 Change the text size (in pixels). 
 textsize 
 Output the current text size (in pixels). 
 setfont name 
 Change the text font. 
 font 
 Output the current text font. 
 
 
 4. Arithmetic 
 4.1 Numeric Operations 
 Inputs are numbers or numeric expressions, output is a number. 
 
 
 sum expr expr 
 (sum expr ... ) 
 expr + expr 
 difference expr expr 
 expr - expr 
 product expr expr 
 (product expr ... ) 
 expr * expr 
 quotient expr expr 
 (quotient expr ) 
 expr / expr 
 power expr expr 
 expr ^ expr 
 Add, subtract, multiply, divide, and raise-to-the-power-of respectively. A single input to quotient returns the reciprocal. 
 remainder expr expr 
 expr % expr 
 modulo expr expr 
 Outputs the remainder (modulus). For remainder and % the result has the same sign as the first input; for modulo the result has the same sign as a the second input. 
 minus expr 
 - expr 
 Unary minus sign must begin a top-level expression, follow an infix operator, or have a leading space and no trailing space. 
 abs num 
 Absolute value 
 int num 
 round num 
 Truncate or round a number, respectively. 
 sqrt expr 
 exp expr 
 log10 expr 
 ln expr 
 Square root, e to the power of, common logarithm, and natural logarithm, respectively. 
 arctan expr 
 (arctan x y ) 
 sin expr 
 cos expr 
 tan expr 
 The usual trig functions. Angles are in degrees. 
 radarctan expr 
 (radarctan x y ) 
 radsin expr 
 radcos expr 
 radtan expr 
 The usual trig functions. Angles are in radians. 
 iseq first last 
 Outputs a list with integers from first to last , inclusive 
 show iseq 1 10 
 rseq first last count 
 Outputs a list of count numbers from first to last , inclusive 
 show rseq 1 9 5 
 
 
 4.2 Numeric Predicates 
 
 
 lessp expr expr 
 less? expr expr 
 expr < expr 
 greaterp expr expr 
 greater? expr expr 
 expr > expr 
 lessequalp expr expr 
 lessequal? expr expr 
 expr <= expr 
 greaterequalp expr expr 
 greaterequal? expr expr 
 expr >= expr 
 Less than, greater than, less than or equal to, greater than or equal to, respectively. Inputs are numbers or numeric expressions, output is 1 (true) or 0 (false). 
 
 
 4.3 Random Numbers 
 
 
 random expr 
 (random start end ) 
 Outputs a random number from 0 through one less than expr , or from start to end inclusive. 
 show random 10 
 show (random 1 6) 
 rerandom 
 ( rerandom expr ) 
 Reseeds the random number generator, either to a fixed value or the specified seed. 
 
 
 4.4 Print Formatting 
 
 
 form expr width precision 
 Outputs a formatted string with the result of a numeric expression with precision decimal places and padded on the left with spaces (if necessary) to be at least width characters long. 
 show form 1/3 10 3 
 
 
 4.5 Bitwise Operations 
 
 
 bitand expr expr 
 (bitand expr ...) 
 bitor expr expr 
 (bitor expr ...) 
 bitxor expr expr 
 (bitxor expr ...) 
 bitnot expr 
 Bitwise and, or, exclusive-or, and not, respectively. 
 ashift expr bitcount 
 Arithmetic bit shift. If bitcount is negative, shifts to the right, preserving sign. 
 lshift expr bitcount 
 Logical bit shift. If bitcount is negative, shifts to the right, zero-filling. 
 
 
 5. Logical Operations 
 
 
 true 
 Outputs 1 
 false 
 Outputs 0 
 and expr expr 
 (and expr ... ) 
 or expr expr 
 (or expr ... ) 
 xor expr expr 
 (xor expr ... ) 
 not expr 
 Logical "and", "or", "exclusive-or", and "not", respectively. Inputs are numbers or numeric expressions, output is 1 (true) or 0 (false). 
 
 
 6. Graphics 
 An introduction to Turtle Geometry . 
 6.1 Turtle Motion 
 
 
 forward expr 
 fd expr 
 Move turtle forward expr pixels 
 fd 100 
 back expr 
 bk expr 
 Move turtle backward expr pixels 
 bk 100 
 left expr 
 lt expr 
 Rotate expr degrees counterclockwise 
 lt 90 
 right expr 
 rt expr 
 Rotate expr degrees clockwise 
 rt 90 
 setpos [ expr expr ] 
 setxy expr expr 
 setx expr 
 sety expr 
 Move turtle to the specified location 
 setpos [ 100 -100 ] 
 setxy -100 100 
 setheading expr 
 seth expr 
 Rotate the turtle to the specified heading 
 setheading 45 
 home 
 Moves the turtle to center, pointing upwards 
 arc angle radius 
 Without moving the turtle, draws an arc centered on the turtle, starting at the turtle's heading. 
 arc 180 100 
 
 
 6.2 Turtle Motion Queries 
 
 
 pos 
 xcor 
 ycor 
 Outputs the current turtle position as [ x y ], x or y respectively 
 show pos 
 heading 
 Outputs the current turtle heading 
 show heading 
 towards [ expr expr ] 
 Outputs the heading towards the specified [ x y ] coordinates 
 show towards [ 0 0 ] 
 scrunch 
 Outputs the current graphics scaling factors 
 show scrunch 
 bounds 
 Outputs the current graphics screen bounds [ xmin xmax ymin ymax ] 
 show bounds 
 
 
 6.3 Turtle and Window Control 
 
 
 showturtle 
 st 
 Show the turtle 
 hideturtle 
 ht 
 Hide the turtle 
 clean 
 Clear the drawing area 
 clearscreen 
 cs 
 Same as clean and home together 
 wrap 
 If the turtle moves off the edge of the screen it will continue on the other side. (default) 
 window 
 The turtle can move past the edges of the screen, unbounded. 
 fence 
 If the turtle attempts to move past the edge of the screen it will stop. 
 fill 
 Does a paint bucket flood fill at the turtle's position. 
 arc 360 100 fill 
 filled fillcolor [ statements ... ] 
 Execute statements without drawing but keeping track of turtle movements. When complete, fill the region traced by the turtle with fillcolor and outline the region with the current pen style. 
 filled "red [ repeat 5 [ fd 100 rt 144 ] ] 
 label expr 
 Draw a word (same logic as print ) on the graphics display at the turtle location 
 repeat 8 [ label "Logo rt 45 ] 
 setlabelheight expr 
 Set the height for text drawn by label , in pixels 
 setlabelheight 100 label "Logo 
 setlabelfont expr 
 Set the font for text drawn by label 
 setlabelfont "Times\ New\ Roman label "Logo 
 setscrunch sx sy 
 Set the graphics scaling factors 
 setscrunch 1 2 arc 360 100 
 setturtle index 
 Switch to the turtle numbered index (starting from 1 for the default turtle present at start). If the turtle has not been used yet, it will be created at the center, facing upwards, visible, with the pen down. 
 setturtle 2 rt 90 fd 100 
 ask turtleindex [ statements ... ] 
 Execute statements as turtle number turtleindex . 
 ask 2 [ rt 90 fd 100 ] 
 clearturtles 
 Remove all turtles, keeping the current one as index 1. 
 fd 50 setturtle 2 rt 90 fd 100 clearturtles 
 
 
 6.4 Turtle and Window Queries 
 
 
 shownp 
 shown? 
 Outputs 1 if the turtle is shown, 0 if the turtle is hidden 
 turtlemode 
 Outputs WRAP , WINDOW or FENCE 
 labelsize 
 Outputs the height of text drawn by label , in pixels 
 labelfont 
 Outputs the name of the font drawn by label 
 turtle 
 Outputs the index of the currently-active turtle 
 turtles 
 Outputs the largest index that has been passed to setturtle 
 
 
 6.5 Pen and Background Control 
 
 
 pendown 
 pd 
 Turtle resumes leaving a trail 
 penup 
 pu 
 Turtle stops leaving a trail 
 penpaint 
 ppt 
 penerase 
 pe 
 penreverse 
 px 
 Change the turtle drawing mode - paint (the default) leaves a colored trail, erase restores the background, reverse inverts the background. 
 setpw 10 px repeat 5 [ fd 100 rt 144 ] 
 setpencolor logocolor 
 setpencolor csscolor 
 setpencolor [ r g b ] 
 Set pen/text color. Color can be a standard Logo color number (0-15), CSS color string ( CSS color names or #rrggbb ), or in the list version, r/g/b values in 0...99. 
 The standard Logo colors are:
 
 
 
 0 black 
 1 blue 
 2 green 
 3 cyan 
 
 
 4 red 
 5 magenta 
 6 yellow 
 7 white 
 
 
 8 brown 
 9 tan 
 10 green 
 11 aqua 
 
 
 12 salmon 
 13 purple 
 14 orange 
 15 gray 
 
 
 
 
 setpencolor 4 
 setpencolor "red 
 setpencolor "#ff0000 
 setpencolor [ 99 0 0 ] 
 setpalette colornumber csscolor 
 setpalette colornumber [ r g b ] 
 Change one of the standard color entries (8 or above) to the given color. 
 setpalette 8 "pink setbg 8 
 setpalette 8 "#ff4f00 setbg 8 
 setpalette 8 [ 99 31 0 ] setbg 8 
 setpensize expr 
 Set pen width in pixels. If expr is a list, the first member is used. 
 setbackground color 
 setscreencolor color 
 setsc color 
 Set the background color; same options as setpencolor 
 setbackground "red 
 
 
 6.6 Pen Queries 
 
 
 pendownp 
 pendown? 
 Outputs 1 if the pen is down, 0 otherwise 
 show pendown? 
 penmode 
 Outputs PAINT , ERASE or REVERSE 
 show penmode 
 pencolor 
 pc 
 Outputs the current pen color. This will be a CSS color string, not necessarily the value passed in. 
 show pencolor 
 palette colornumber 
 Outputs the a palette entry. This will be a CSS color string, not necessarily the value passed in. 
 show palette 8 
 pensize 
 Outputs a two element list with the pen width and height (usually the same). 
 show pensize 
 background 
 bg 
 getscreencolor 
 getsc 
 Outputs the background color. This will be a CSS color string, not necessarily the value passed in. 
 show background 
 
 
 6.7 Bitmap Operations 
 
 
 bitcut width height 
 Copy a bitmap, from the turtle's position width by height pixels. 
 bitpaste 
 Paste the previously copied bitmap at the current turtle position. 
 repeat 4 [ rt 90 fd 40 ] bitcut 50 50 pu fd 100 bitpaste 
 
 
 6.8 Mouse/Touch Queries 
 
 
 mousepos 
 Outputs a list of the x, y coordinates of the last mouse position 
 forever [setpos mousepos] 
 clickpos 
 Outputs a list of the x, y coordinates of the last mouse press 
 forever [setpos clickpos] 
 buttonp 
 button? 
 Outputs 1 if any mouse button is down, 0 otherwise. 
 forever [ifelse button? [pd] [pu] setpos mousepos] 
 button 
 Outputs a number indicating the pressed mouse buttons ( 1 = left, 2 = right, etc) or 0 for none. 
 touches 
 Outputs a list of current touch coordinates 
 forever [ifelse count touches [setpos first touches pendown] [penup]] 
 
 
 7. Workspace Management 
 7.1 Procedure Definition 
 
 
 to procname inputs ... statements ... end 
 Define a new named procedure. Inputs can be:
 
 Required: :a :b 
 Optional (with default values): [:c 5] [:d 7] 
 Rest (remaining inputs as a list): [:r] 
 Default number of inputs: 3 
 
 
 to star :n repeat 5 [ fd :n rt 144 ] end 
 define procname [[ inputs ...][ statements ...]] 
 Define a new named procedure with optional inputs 
 define "star [[n][repeat 5 [fd :n rt 144]]] 
 def procname 
 Outputs the definition of a named procedure as a string 
 show def "star 
 text procname 
 Outputs the definition of a named procedure as a list, suitable for use with DEFINE 
 show text "star 
 copydef newname oldname 
 Copy a procedure. If a procedure newname already existed it will be overridden. Primitive procedures can't be overridden unless REDEFP is TRUE . 
 copydef "new "old 
 
 
 7.2 Variable Definition 
 
 
 make varname expr 
 Update a variable or define a new global variable. The variable name must be quoted 
 make "myvar 5 
 name expr varname 
 Like make but with the inputs reversed 
 name 5 "myvar 
 local varname 
 (local varname ...) 
 A subsequent make will create the variable(s) in the local scope instead of the global scope 
 local "myvar 
 localmake varname expr 
 Define a variable in the local scope (shortcut for local then make 
 localmake "myvar 5 
 thing varname 
 Outputs the value of variable. :foo is a shortcut for thing "foo 
 show thing "myvar 
 global varname 
 Reserve the variable at the global scope. This doesn't do anything useful. 
 global "myvar 
 
 
 7.3 Property Lists 
 
 
 pprop plistname propname value 
 Set the property propname in the property list plistname to value value. 
 gprop plistname propname 
 Get the value of the property propname in the property list plistname , or the empty list if no such property. 
 remprop plistname propname 
 Remove the property propname in the property list plistname . 
 plist plistname 
 Return a list of properties in the property list plistname , alternating property name, property value. 
 
 
 7.4 Workspace Predicates 
 Predicates return 1 (true) or 0 (false) 
 
 
 procedurep name 
 procedure? name 
 Test if there is a procedure with the given name. 
 primitivep name 
 primitive? name 
 Test if there is a built-in procedure with the given name. 
 definedp name 
 defined? name 
 Test if there is a user-defined procedure with the given name. 
 namep name 
 name? name 
 Test if there is a variable with the given name. 
 plistp name 
 plist? name 
 Test if there is a property list with the given name. 
 
 
 7.5 Workspace Queries 
 
 
 contents 
 Outputs a list with three members. The first is a list of user-defined procedure names. The second is a list of defined variables. The third is a list of non-empty property list names. Only non-buried procedures, variables, and property lists are included. 
 buried 
 Outputs a list with three members. The first is a list of user-defined procedure names The second is a list of defined variables. The third is a list of non-empty property list names. Only buried procedures, variables, and property lists are included. 
 procedures 
 Outputs a list of user-defined non-buried procedure names. 
 primitives 
 Outputs a list of primitive non-buried procedure names. 
 globals 
 Outputs a list of defined non-buried global variables. 
 names 
 Outputs a list with two members. The first is an empty list. The second is a list of defined non-buried variables. 
 plists 
 Outputs a list with three members. The first is an empty list. The second is an empty list. The third is a list of non-empty non-buried property list names. 
 namelist name 
 namelist namelist 
 Return a contents -style list with the given variable names. 
 pllist plname 
 pllist plnamelist 
 Return a contents -style list with the given property lists. 
 arity procname 
 Return a list with the procedure's minimum, default, and maximum number of inputs; maximum is -1 if unlimited. 
 
 
 7.7 Workspace Control 
 
 
 erase contentslist 
 Takes a three member list, where the first is a list of user-defined procedure names to erase, the second is a list of defined variables to erase, the third is a list of property lists to erase. Primitive procedures can't be erased unless REDEFP is TRUE . 
 erase [ [myproc] [myvar] [] ] 
 erall 
 Erase all non-buried user-defined procedures, variables and property lists. 
 erps 
 Erase all non-buried user-defined procedures. 
 erns 
 Erase all non-buried variables. 
 erpls 
 Erase all non-buried property lists. 
 ern varname 
 ern varnamelist 
 Erase the named variable(s). 
 epl plname 
 epl plnamelist 
 Erase the named property list(s). 
 bury contentslist 
 Takes a three member list, where the first is a list of user-defined procedure names to bury, the second is a list of defined variables to bury, the third is a list of property lists to bury. 
 buryall 
 Bury all user-defined procedures, variables, and property lists. 
 buryname varname 
 buryname varnamelist 
 Bury the given variable (or list of variables). 
 unbury contentslist 
 Takes a three member list, where the first is a list of user-defined procedure names to unbury, the second is a list of defined variables to unbury, the third is a list of property lists to unbury. 
 unburyall 
 Unbury all user-defined procedures, variables, and property lists. 
 unburyname varname 
 unburyname varnamelist 
 Unbury the given variable (or list of variables). 
 buriedp contentslist 
 buried? contentslist 
 Return 1 if the first named user-defined procedure, variable, or property list exists and is buried, 0 otherwise. 
 
 
 8. Control Structures 
 8.1 Control 
 
 
 run [ statements ... ] 
 Run the specified statements once 
 run [ fd 100 rt 90 ] 
 runresult [ statements ... ] 
 Run the specified statements once. If the statements return a value, the result is a list with the value as a single member. Otherwise, the result is an empty list. 
 repeat expr [ statements ... ] 
 Repeat statements expr times 
 repeat 4 [ fd 100 rt 90 ] 
 forever [ statements ... ] 
 Repeat statements forever. Used inside a user-defined procedure that terminates with output , stop or bye 
 forever [ make "n random 100 show :n if :n == 0 [ bye ] ] 
 repcount 
 # 
 Outputs the current iteration number of the current repeat or forever 
 repeat 10 [ show repcount ] 
 repeat 10 [ show # ] 
 if expr [ statements ... ] 
 if [ expr ] [ statements ... ] 
 Execute statements if the expression is non-zero 
 if 2 > 1 [ show "yep ] 
 ifelse expr [ statements ... ] [ statements ... ] 
 ifelse [ expr ] [ statements ... ] [ statements ... ] 
 Execute first set of statements if the expression is non-zero, otherwise execute the second set 
 ifelse 1 > 2 [ show "yep ] [ show "nope ] 
 test expr 
 test [ expr ] 
 Test the specified expression, save the result in the local scope for subsequent use by iftrue or iffalse 
 iftrue [ statements ... ] 
 ift [ statements ... ] 
 iffalse [ statements ... ] 
 iff [ statements ... ] 
 Run the statements if the result of the last local test was non-zero (true) or zero (false) respectively. 
 test 1 > 2 iftrue [ show "yep ] iffalse [ show "nope ] 
 stop 
 End the running procedure with no output value. 
 output expr 
 op expr 
 End the running procedure and output the specified value. 
 catch tag instructionlist 
 Run instructions, but if an error with matching tag is thrown, return the thrown value (if any). Use "ERROR to catch errors from regular procedures. 
 catch "t [ show "before throw "t show "after ] 
 catch "error [ show 1 / 0 ] show error 
 throw tag 
 (throw tag value) 
 Throw an error with the given tag which may be caught. An optional return value can be passed. 
 show catch "t [ show "hello (throw "t "world) ] 
 error 
 Outputs a list describing the last error caught: an error number, an error message message, and the procedure name where the error occurred. 
 catch "error [ show 1 / 0 ] show error 
 wait time 
 Pauses execution. time is in 60ths of a second. 
 bye 
 Terminate the program 
 .maybeoutput expr 
 Like output if expr returns a value, like stop otherwise 
 ignore expr 
 Evaluate and ignore results of the expression 
 make "q [ 1 2 3 ] ignore dequeue "q 
 ` list 
 Outputs the list with substitutions:
 
 , instructionlist replaced by output 
 ,@ instructionlist replaced by output list members 
 ", instruction replaced by output prefixed with " 
 ,@ instruction replaced by output prefixed with : 
 
 
 show `[a b ,[bf [c d e]] f ,@[bf [g h i]]] 
 make "v "x show `[",:v :,:v] 
 for controllist [ statements ... ] 
 Typical for loop. The controllist specifies three or four members: the local varname , start value, limit value, and optional step size. 
 for [ a 1 10 ] [ show :a ] 
 for [ a 0 20 2 ] [ show :a ] 
 dotimes [ varname times ] [ statements ... 
 Run the statements the specified number of times . The variable varname is set to the current iteration number. 
 dotimes [ i 5 ] [ show :i * :i ] 
 do.while [ statements ... ] expr 
 do.while [ statements ... ] [ expr ] 
 Runs the specified statements at least once, and repeats while the expression is non-zero (true). 
 do.while [ make "a random 10 show :a ] :a < 8 
 while expr [ statements ... ] 
 while [ expr ] [ statements ... ] 
 Runs the specified statements only while the expression remains non-zero (true). 
 while (random 2) = 0 [ show "zero ] show "one 
 do.until [ statements ... ] expr 
 do.until [ statements ... ] [ expr ] 
 Runs the specified statements at least once, and repeats while the expression is zero (false). 
 do.until [ make "a random 10 show :a ] :a < 8 
 until expr [ statements ... ] 
 until [ expr ] [ statements ... ] 
 Runs the specified statements only while the expression remains zero (false). 
 until (random 2) = 0 [ show "one ] show "zero 
 case value [ clauses ... ] 
 For each clause in order: If the clause is of the form [ ELSE expr ] then expr is evaluated and returned. Otherwise, if the clause is of the form [ [ matches ] expr ] and value is a member of matches then expr is evaluated and returned. 
 show case :var [ [ ["a] "AAA ] [ ["b] "BBB ] [ else "other ] ] 
 cond [ clauses ... ] 
 For each clause in order: If the clause is of the form [ ELSE expr ] then expr is evaluated and returned. Otherwise, if the clause is of the form [ [ expr1 ] expr2 ] and expr1 evaluates to non-zero (true) then expr2 is evaluated and returned. 
 show cond [ [ [:var = 1] "one] [ [:var = 2] "two] [ else "other ] ] 
 
 
 8.2 Template-based Iteration 
 These higher-level procedures support only the named procedure form of template. The first input is the name of a procedure to call. 
 
 
 apply procname list 
 Call procname with the members of list as inputs 
 invoke procname input1 
 (invoke procname input1 ...) 
 Call procname with the specified inputs as inputs 
 invoke "show "hello 
 foreach list procname 
 call procname for each item in the list 
 foreach [1 2 3] "show 
 map procname list 
 Outputs a list composed of the results of calling procname for each item in the list 
 to double :n output :n * 2 end show map "double [1 2 3] 
 filter procname list 
 Outputs a list composed of the input list where procname called on the item returns non-zero (true) 
 to oddp :n output bitand :n 1 end show filter "oddp [ 1 2 3 4 5 ] 
 find procname list 
 Outputs the first item in list for which calling procname on it returns non-zero (true). If not found, the empty list is returned. 
 to oddp :n output bitand :n 1 end show find "oddp [ 2 8 4 7 10 9 ] 
 reduce procname list 
 (reduce procname list initial ) 
 Call procname repeatedly with two inputs - the current value and the next list item. If initial is not specified, the first list element is used instead. 
 show reduce "sum [ 1 2 3 4 5 ] 
 crossmap procname listlist 
 (crossmap procname list list ...) 
 Call procname repeatedly with inputs from the lists, in all possible combinations. 
 show crossmap "word [[a b] [x y]] 
 show (crossmap "word [a b c] [1 2 3 4])