This is a very minimal Lisp-like language that I wrote about 8 years ago as an extension language for another project.
I wrote this when I was learning OCaml, so there are some things that probably look a bit strange. Looking at it again I'd do things differently if I was doing this today, but hopefully it's interesting or useful to somebody.
Install ocamlbuild, then run ocamlbuild -libs unix,dynlink main.byte, or just type make (which runs ocamlbuild).
Run ./main.byte to get a read-eval-print loop:
#> (+ 1 2)
3
#> (defun fib (n)
(cond
((<= n 1) 1)
(t (+ (fib (- n 1)) (fib (- n 2))))))
fib
#> (mapcar #'fib '(1 2 3 4 5))
(1 2 3 5 8)