AutoLISP is a programming language designed for extending and customizing AutoCAD 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.
AutoCAD 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.
Visual LISP (VLISP) is a software tool designed to expedite AutoLISP program development. The VLISP integrated development environment (IDE) provides features to help ease the tasks of source-code creation and modification, program testing, and debugging. In addition, VLISP provides a vehicle for delivering standalone applications written in AutoLISP.
In the past, developing AutoLISP programs for AutoCAD meant supplying your own text editor for writing code, then loading the code into AutoCAD and running it. Debugging your program meant adding statements to print the contents of variables at strategic points in your program. You had to figure out where in your program to do this, and what variables you needed to look at. If you discovered you still didn't have enough information to determine the error, you had to go back and change the code again by adding more debugging points. And finally, when you got the program to work correctly, you needed to either comment out or remove the debugging code you added.