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2. Data Structure Primitives


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2.1 Constructors


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word

 
WORD word1 word2
(WORD word1 word2 word3 ...)

outputs a word formed by concatenating its inputs.


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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).


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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.


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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.


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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.


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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 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 section item , setitem , print .


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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].


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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.


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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.


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combine

 
COMBINE thing1 thing2				(library procedure)

if thing2 is a word, outputs WORD thing1 thing2. If thing2 is a list, outputs FPUT thing1 thing2.

See section word , fput


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reverse

 
REVERSE list					(library procedure)

outputs a list whose members are the members of the input list, in reverse order.


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gensym

 
GENSYM						(library procedure)

outputs a unique word each time it's invoked. The words are of the form G1, G2, etc.


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2.2 Data Selectors


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first

 
FIRST thing

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).


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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 section map , map.se , foreach


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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.


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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.


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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

but is provided as a primitive in order to speed up the iteration tools MAP, MAP.SE, and FOREACH.

See section map , map.se , foreach


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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.


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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.


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mditem

 
MDITEM indexlist array				(library procedure)

outputs the member of the multidimensional array selected by the list of numbers indexlist.


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pick

 
PICK list					(library procedure)

outputs a randomly chosen member of the input list.


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remove

 
REMOVE thing list				(library procedure)

outputs a copy of list with every member equal to thing removed.


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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.


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quoted

 
QUOTED thing					(library procedure)

outputs its input, if a list; outputs its input with a quotation mark prepended, if a word.


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2.3 Data Mutators


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setitem

 
SETITEM index array value

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.


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mdsetitem

 
MDSETITEM indexlist array value			(library procedure)

command. Replaces the member of array chosen by indexlist with the new value.


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.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 non-experts 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.


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.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.


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.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 non-experts is not recommended. The use of .SETITEM can lead to circular arrays, which will get some Logo primitives into infinite loops.

See section setitem.


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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.


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pop

 
POP stackname					(library procedure)

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.


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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.


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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.


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2.4 Predicates


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wordp

 
WORDP thing
WORD? thing

outputs TRUE if the input is a word, FALSE otherwise.


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listp

 
LISTP thing
LIST? thing

outputs TRUE if the input is a list, FALSE otherwise.


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arrayp

 
ARRAYP thing
ARRAY? thing

outputs TRUE if the input is an array, FALSE otherwise.


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emptyp

 
EMPTYP thing
EMPTY? thing

outputs TRUE if the input is the empty word or the empty list, FALSE otherwise.


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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 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 section caseignoredp , setitem


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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.


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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 section caseignoredp , lessp


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.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 non-experts is not recommended. The use of mutators can lead to circular data structures, infinite loops, or Logo crashes.


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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 section equalp .


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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 section equalp .


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numberp

 
NUMBERP thing
NUMBER? thing

outputs TRUE if the input is a number, FALSE otherwise.


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vbarredp

 
VBARREDP char
VBARRED? char
BACKSLASHEDP char                               (library procedure)
BACKSLASHED? char                               (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.


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2.5 Queries


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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.)


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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.)


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rawascii

 
RAWASCII char

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.


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char

 
CHAR int

outputs the character represented in the ASCII code by the input, which must be an integer between 0 and 255.

See section ascii .


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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 section memberp .


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lowercase

 
LOWERCASE word

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


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uppercase

 
UPPERCASE word

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


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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 

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.


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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 section readlist , readword


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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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This document was generated by Brian Harvey on September, 3 2008 using texi2html 1.78.