Reverse Polish LISP

Reverse Polish LISP (or alternatively Reverse Polish Language) is the programming language used on modern Hewlett-Packard calculators, such as the HP-48. The similarities to actual LISP are very limited; RPL does not even share LISP's heavy use of parentheses. RPL actually resembles Forth more than any other programming language, due to their similar "stack-oriented," RPN-based operation.