I've been interested in programming languages for a while, and Haskell for a subset of that time. What better way to explore both than writing compilers and interpreters in Haskell? This interpreter is based on Write Yourself a Scheme.
This project required application of a lot of fun Haskell concepts, including parsing to an AST with Parsec, using monad transformers (for Error handling and IO), using IORef (for nested Lisp environments), and more.
Compile Lisp.hs with GHC. You can run files with ./Lisp filename.lsp or start up the REPL with ./Lisp
There's a small standard library in stdlib.lsp. To use it, run (load "stdlib.lsp")
An example session:
ghc Lisp.hs
./Lisp
Lisp> (+ 1 2 2 2)
7
Lisp> (define x 1)
1
Lisp> (+ x 1)
2
Lisp> (map (curry + 1) '(1 1 1 1))
Getting an unbound variable: map
Lisp> (load "stdlib.lsp")
(lambda ("pred" "lst") ...)
Lisp> (map (curry + 1) '(1 1 1 1))
(2 2 2 2)
Lisp> quit