Logo Arts

Argument
A number, word or list passed to a primitive or procedure. Arguments appear immediately after the primitive or procedure name.

ASCII
American Standard Code for Information Interchange. Has been superseded by Unicode.

Boolean
A value which is limited to either true or false. True is represented as “true or 1. False is represented as “false or 0. Boolean values can be added, subtracted or multiplied. Division is avoided as easily creates divide by zero error.

Case
Keyboard letters can be entered as either lower or upper case. Eg 'a' or 'A'. XLogo is not case sensitive, so, setpencolor is the same as SetPenColor.

Character
A single letter, numeric digit, punctuation mark, or space. Each character has a unique Unicode number.

Code
A series of instructions or procedures making up an xLogo program.

Command Line
A text entry field for typing in a single line command for xLogo to execute.

Comment
Information added to a program to help users better understand the code. Comments are ignored by XLogo. They are designated with a '#' symbol.

Decrement
Decrease a numerical value by one.

Element
A number, word or list.

Editor
Short for text editor. Window where procedures can be written and edited.

Error Message
A message to the user about something that went wrong. Printed in red in the Text window.

Execute
To execute a program or instruction is to run it. Once you type a Logo instruction into the command line, press the Enter (or Return) key to execute that instruction.

Increment
Increase a numerical value by one.

Indent
Add extra space at the beginning of a line of code to move it over and so make the program easier to follow.

Input
A number, word or list passed to a primitive or procedure. Inputs appear immediately after the primitive or procedure name.

Instruction
One or more Logo commands typed onto a single line.

Integer
A whole number value. No decimal or fractional part.

Iteration see Loop

Library
A file containing a number of common procedures (or pseudo primitives) which are added at XLogo start up.

List
A series of elements (numbers, words or lists) enclosed in square brackets.

Logo
A programming language invented over thirty years ago to make it easier to learn programming.

Loop
A list of instructions that is repeated (or iterated) in a program. They may be repeated a set number of times or repeated as long as a certain condition is true.

Operation
A primitive or procedure, that outputs a value.

Optional Arguments
An argument that can be omitted. eg If the Step size is not declared when using the For primitive, a step size of 1 is assumed.

Optional arguments can be added to any procedure by enclosing in square brackets. To use, enclose the procedure name and all arguments in normal brackets. See Yin shape.

Parameters see Inputs

Predicates
A primitive or procedure which returns either True of False.

Primitive
An XLogo built in command. May require none, one or more arguments. Eg Forward 44 requires a single numeric argument.

Procedure
A series of commands written by the user. Assigned a unique name. May require none, one or more arguments.

Program
One or more Logo primitives or procedures which are saved together and named.

Pseudo Primitive
A primitive added to a start up file and so always available within XLogo.

Run see Execute

String
A series of ASCII characters one after the other. A word, sentence, or number.

Text Window
Text area showing command line entries, print output statements and error messages.

Transparent
A procedure is transparent if it leaves the state of the turtle (position heading etc) unaltered when finished. Good practice to create transparent procedures as they can be used in any order without affecting each other.

Unicode
A unique number representing each keyboard/screen character. eg Unicode "A = 65.

User
The person using the computer program. That’s you!

User Input
Information coming into a computer from the outside world. Usually key presses from keyboard or mouse movement.

Variable
Container holding a number, word or a list. Variables are named and can be passed from one procedure to another. The contents of a variable can be read or changed.