List Introduction
Mar 06
Functions
LISP is an acronym for LISt Processing and is a programming language that consists of only three elements: atoms, lists, and functions. An atom is the basic unit of any LISP program, simple defined as a single computer word or element. You could say that atoms represent the basic building elements of data in LISP.
A Function can be defined as a LISP program which always returns a result. Functions may be user defined or already built into AutoLISP such as the common math functions +, -, *, and /. Each function is called simply by giving its name as the first element of a list, with any arguments to that function as the subsequent elements of the list.
A list therefore, is a group of atoms that are contained within an opening parenthesis “(” and a closing parenthesis “)”. These lists may contain any number of reals, integers, strings, variables, or other lists and are treated as one expression stored in a single variable. Lists can be used to organize and process groups of information.
Sample list’s are:
(“A” “B”) ;;two elements
(table) ;;one element
((desk chair) (files)) ;;two elements
(1 (2 3) “test” (c d)) ;;four elements
Point Lists
Graphic coordinates such as 2D points are expressed as a list of two real numbers
(X Y), as in:
(12.435678 7.134000)
3D coordinates are expressed in the same manner with the third value of the list being the Z coordinate.
(12.435678 7.134000 1.000000)
This predefined structure, referred to as a point list, accommodates the interface between AutoLISP and AutoCAD.
