HAL/S

HAL/S, short for High-order Assembly Language/Shuttle, is a real-time aerospace programming language and compiler used for avionics software by NASA and associated agencies such as JPL. Intermetrics designed it in 1972 for NASA and delivered it in 1973. Its most significant use was the Space Shuttle program, where roughly 85 percent of the flight software was written in HAL/S. Its designers stressed reliability, efficiency and machine independence, and wanted aerospace tasks such as vector and matrix arithmetic to be readable by people who know spaceflight but are not expert programmers. To avoid known sources of error it has no dynamic memory allocation, and it gives special support to real-time execution. A notable syntax feature is an optional three-line input format in which the first and third lines carry superscripts and subscripts, so code can resemble mathematical notation. HAL/S has native integers, floating point scalars, vectors, matrices, booleans and strings of up to 255 characters, and its compiler is itself written in XPL, a dialect of PL/I. The name honors Hal Laning of the Draper Laboratory. Host compilers ran on the IBM 360 and 370, and targets included the IBM AP-101 shuttle computer.