MCL is an object-oriented dynamic programming language fully integrated with the Macintosh. It implements the current industry standard Common Lisp programming language and CLOS (as defined in Common Lisp: The Language, Second Edition). It includes: an incremental compiler which generates efficient native PowerPC code; a fully integrated emacs-like Lisp program editor; a window-based debugger; a source code stepper; a dynamic object inspector; smart Lisp programming tools; and an extensive library of CLOS objects including Macintosh user interface objects.