Productivity measured against what quality metric? For getting code written fast, Lisp is pretty good. For writing an operating system on which you can run a web server that will be competitive with nginx on Linux in terms of requests-per-second, probably not so much.
Maturity? Gets out of the way? Advanced documentation/learning material? Wealth of prior work solutions to common patterns? It's not so hard to guess what any developer's productivity is hinged on.
I asked because many people that used them called out the machines as being very productive...above and beyond lisp. Another comment here suggests it might have been CLIM.
Ah. A lot of that was because the LispMs had really good IDEs at a time when IDEs were all but unheard of. This was possible because it's a lot easier to write an IDE for Lisp than for C. But all that can be re-created at the application level (obviously because IDEs are applications). There's no need for a system-level Lisp to get that win.
In fact, Clozure Common Lisp is a perfect example. It provides (IMHO) 80-90% of the productivity advantages of a LispM when you run it on a Mac (because the IDE is Mac-specific).
