Lisp in fewer than 200 lines of C
Writing your own Lisp-ette is a brilliant evening or weekend project, regardless of the language. It's some of the simplest non-toy parsing you can attempt, a bit of light data structure work, and understanding eval/apply is 80% of the work in implementing it. I would highly recommend anyone to have a go, and try not to follow existing code too closely: figure out the problems in your language of choice.The post identifies some of it's own weaknesses (memory handling, errors), which are quite C specific. Or at least easier to handle in other languages, where you can punt those issues to the host language runtime. But it will be a fun extension to fix them (a job for the second evening / weekend of coding ;) )But, imho, the beauty of writing a Lisp is that there are a bunch of things you can do from there, some more difficult, but several are achievable step-by-step in a day or a few days each. I'd first add a few special forms more than the OP (quote, if, progn, math operations), then my suggestions:1. Defining names (if you haven't already), both let and define special forms.2. Lambdas.3. Tail call optimisation (I suggest this not because it's an optimisation, this Lisp doesn't need optimising, but because TCO is a bite-sized extension.)4. Lexical scoping of lambdas.5. Continuations. call/cc6. And if you're really brave (or skilled, or just masochistic), macros.I was encouraged to do this as a new grad student, and it was one of the most fun and educational experiences I remember. I didn't get as far as macros back then, but implementing call/cc was a definite pivot point in my programming competence.