Glossary

Array

A primitive data type that is an ordered set of zero or more things. For example, {123 abc} is an array with two members. Arrays are similar to lists, except you can easily change the items within an array, but you can't easily create a new array that is everything after a specified item. That is, SETITEM works, but BUTFIRST doesn't. In general, procedures operator on arrays are faster than equivalent procedures operate on lists.

Command

A procedure that does not output a value.

Color Vector

A list of three numbers that represents the magnitude of red, green, and blue that are associated with a particular color. The numbers within the list must be integers from 0 to 255, inclusive. Wherever a colorvector is accepted as input, you may also supply a color index.

Contents List

A list of three lists, which respectively contains the names of all procedures, variables, and property lists within a workspace. Contents lists are sometimes abbreviated by omitting the list of things that are irrelevant in a particular context. For example, [[SQUARE TRIANGLE] [myvar] [myplist]] is a contents list for a workspace that contains two procedures (SQUARE and TRIANGLE), a variable (myvar), and a property list (myplist). If you were only interested in the variables, then the contents list could be abbreviated to [[] [myvar]]. Note that you can't remove a list that comes before the one you're interested in, so the list of procedure names still appears, even though it is empty. You can remove a list that comes after the one you're interested in, so the list of property lists is omitted.

Element

An item of an array that is indexed based on the physical layout in memory, instead of by its origin. For example, in the array {a b c}@0, b is the first item, but the second element.

Form

A series of tokens that is syntactically correct for evaluation in Logo.

Expression

A series of tokens that, when RUN, produces a value. This include operations with all of its inputs, as well constant expressions like 3 or "foo.

Instruction

A series of tokens that that, when RUN, produces no value. Generally, this is a command with all of its inputs.

Item

An indexed thing that is contained within a word, a list, or an array. For example, the third item of "abcd is "c. Items are usually called members when their location within a word or list is unimportant.

List

A primitive data type that is an ordered sequence of zero or more things. For example, [123 abc] is a list with two members.

Instruction List

A list of words that are intended to be RUN by some other command. These should be well-formed expressions or instructions, depending on if the procedure that runs the instructionlist expects an output or not.

Member

A thing that is contained within a word or list. For example "c is a member of "abcd. Members are usually called items when their location within a word or list is signficiant.

Operation

A procedure that outputs a value.

Procedure

A named collection of instructions that peforms some task. Procedures that output a value are called operations. Procedures that don't output a value are called commands.

Run

The process of evaluating one or more instructions or expressions and performing all of the side-effects associated with them.

Special Form

A series of tokens that is syntactically correct for evaluation in Logo, but whose meaning is determined by a special rule rather than by the default rule of running it as an instruction or expression.

Word

A primivite data type that is a sequence of characters. This includes constants, like "foo and numbers, like 3.14.


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