What’s so great about Lisp? This question is frequently asked by people who wonder what such a weird-looking language could offer.
The usual response is often “macros.” As a one-liner, this is probably a fair answer. However, it’s not very enlightening, since the questioner isn’t going to have any idea what a Lisp macro is, or what it can do. Telling someone that penicillin is great because it is an antibiotic isn’t very useful if the questioner has no idea what bacteria are or what role they play in causing illness.
The thing *I* like best about using Lisp is that it’s interactive.
My current project is a Mac OS X application written in Objective-C. I am using Apple’s Xcode developement environment, which contains numerous fancy features.
Yet, I still have an emacs running, talking to an inferior lisp via SLIME.
Sometimes I use the lisp as a calculator. Sometimes I’ll get a function working in Lisp and then re-write it in C for insertion into my application. Sometimes I’ll re-write some troublesome C function in Lisp and debug it from the lisp.
Having the ability to do this sort of work interactively and incrementally is a real pleasure. No recompiling files, no special debugger commands, just the whole Lisp environment at your fingertips all the time.