AutoLISP

AutoLISP is a dialect of the LISP programming language built specifically for use with the full version of and its derivatives, which include , and . Neither the application programming interface nor the interpreter to execute AutoLISP code are included in the AutoCAD LT product line.

AutoLISP is a small, dynamically scoped, dynamically typed LISP dialect with garbage collection, immutable list structure and settable symbols, lacking in such regular LISP features as macro system, records definition facilities, arrays, functions with variable number of arguments or let bindings. Aside from the core language, most of the primitive functions are for geometry, accessing AutoCAD's internal DWG database, or manipulation of graphical entities in AutoCAD. The properties of these graphical entities are revealed to AutoLISP as association lists in which values are paired with AutoCAD "group codes" that indicate properties such as definitional points, radii, colors, layers, linetypes, etc. AutoCAD loads AutoLISP code from .LSP files.

AutoLISP code can interact with the user through AutoCAD's graphical editor by use of primitive functions that allow the user to pick points, choose objects on screen, input numbers and other data. AutoLisp also has a built-in GUI mini-language, the Dialog Control Language, for creating modal dialog boxes with automated layout, within AutoCAD.

AutoLISP was derived from an early version of XLISP, which was created by David Betz. The language was introduced in AutoCAD Version 2.18 in January 1986, and continued to be enhanced in successive releases up to Release 13 in February 1995. After that, its development was neglected by Autodesk in favor of more fashionable development environments like VBA, .NET and ObjectARX. However, it has remained AutoCAD's primary user customization language.

...
Wikipedia