RPL (programming language)

RPL is a programming language and calculator operating system developed at Hewlett-Packard's Corvallis, Oregon facility from 1984 for its scientific graphing calculators. It is a structured language based on Reverse Polish Notation, implemented as a threaded interpreter, and it shares ideas with the stack-based Forth and the list-based Lisp. Unlike earlier HP calculators with a fixed four-level stack, RPL uses a dynamic stack limited only by available memory. It first reached users in the HP 28C in 1986 and was used across the HP 28, 48, 49 and 50 series, and internally in several other models. It comes in a high-level User RPL form for application programs and a lower-level System RPL form used to implement the operating system. The last RPL pocket calculator, the HP 50g, was discontinued in 2015, though emulators and community projects such as newRPL and DB48X continue the language.