Common Lisp was (per the name) designed to provide a migration path for a bunch of mutually incompatible LISP dialects that existed in the 1980s, but it wasn't

Common Lisp was (per the name) designed to provide a migration path for a bunch of mutually incompatible LISP dialects that existed in the 1980s, but it wasn't fully compatible with any of them -- programs originally written for even MacLisp/ZetaLisp (the closest relatives) could take substantial work to port. See Pitman's post on Macsyma on this thread, for example: https://groups.google.com/forum/#!topic/comp.lang.lisp/fY92ojHzE4o https://groups.google.com/forum/#!topic/comp.lang.lisp/fY92o...