An interpreter for LISP with support for the predefined functions like PLUS, MINUS, TIMES, EQ, LESS, GREATER ATOM, QUOTE, CDR, CAR, NULL COND, CONS and user-defined functions.
(PLUS (PLUS 3 5) (TIMES 4 4)) (DEFUN DIFF (X Y) (COND ( (EQ X Y) NIL ) (T T) ) ) )
(DIFF 5 6)
(DEFUN MEM (X LIST) (COND ( (NULL LIST) NIL ) ( T (COND ( (EQ X (CAR LIST)) T ) ( T (MEM X (CDR LIST)))))))
(MEM 3 (QUOTE (2 3 4)))