RPL (programming Language)

RPL (programming Language)

The RPL programming language (RPL meaning ROM-based procedural language following Hewlett-Packard or, alternatively, Reverse Polish LISP) is a handheld calculator system and application programming language used on Hewlett-Packard's engineering graphing RPN calculators of the HP-28, HP-48, HP-49 and HP-50 series, but it is also usable on non-RPN calculators, such as the HP-39 series.

RPL is a structured programming language based on RPN but equally capable of processing algebraic expressions and formulae, implemented as a threaded interpreter. RPL has many similarities to Forth, both languages being stack-based, and of course the list-based LISP. Contrary to previous HP RPN calculators, which had a fixed four-level stack, the stack used by RPL is only limited by available calculator RAM.

RPL originated from HP's Corvallis, Oregon development facility in 1984 as a replacement for the previous practice of implementing the operating systems of calculators in assembly language. According to a quote by Dr. William Wickes, one of the original RPL developers, "the development team never calls it anything but (the initials) RPL."