AutoLISP is a programming language designed for extending and customizing AutoCAD product functionality.
It is based on the LISP programming language, whose origins date back to the late 1950s. LISP was originally designed for use in Artificial Intelligence (AI) applications, and is still the basis for many AI applications.
Autodesk introduced AutoLISP as an application programming interface (API) in Release 2.1, in the mid-1980s. LISP was chosen as the initial AutoCAD API because it was uniquely suited for the unstructured design process of AutoCAD projects, which involved repeatedly trying different solutions to design problems.
AutoLISP programs are developed using a basic ASCII text editor, such as NotePad on Windows or TextEdit on Mac OS, or the Visual LISP (VLISP) integrated development environment (IDE) on Windows only. The Visual LISP integrated development environment (IDE) provides features to help ease the tasks of source-code creation and modification, program testing, and debugging.
After an AutoLISP program is written, it must loaded into the product before it can be used or debugged. Debugging your program allows you to evaluate and verify the code is working as expected, and if not identify what might be going wrong. The basics of debugging involve adding statements to the code and reviewing the contents of variables at strategic points in the program. If you discover you still do not have enough information to determine the error, you change the code again by adding additional debugging points. And finally, when you get the program working, you can either comment out or remove the debugging code.