A lisp implementation (with a repl) built on top of Daniel Holden's (theorangeduck) mpc parsing library. Works on Windows and Unix machines.
gcc mpc.c repl.c -lm -ledit -o repl
-lm and -ledit are packages required to run the language. You may need to install these.
./repl
def
to declare variables.def {a-m} (\ {x y} {+ x y})