HAL/S is a real-time aerospace programming language, best known for its use in the Space Shuttle program. It was designed by Intermetrics in the 1970s for NASA. HAL/S is written in XPL, a dialect of PL/I. The three key principles in designing the language were reliability, efficiency, and machine-independence. The language is designed to allow aerospace-related tasks to be accomplished in a way that is easily understandable by people who have spaceflight knowledge, but may not necessarily have proficiency with computer programming. HAL/S was designed not to include some constructs that are thought to be the cause of errors. For instance, there is no support for dynamic memory allocation. The language provides special support for real-time execution environments. Some features, such as "GOTO" were provided chiefly to ease mechanical translations from other languages.