FOCAL (programming language)

FOCAL (acronym for Formulating On-line Calculations in Algebraic Language,^[1] or FOrmula CALculator^[2]) is an interactive interpreted programming language based on JOSS and mostly used on Digital Equipment Corporation (DEC) Programmed Data Processor (PDP) series machines.

JOSS was designed to be a simple interactive language to allow programs to be easily written by non-programmers. FOCAL is very similar to JOSS in the commands it supports and the general syntax of the language. It differs in that many of JOSS' advanced features like ranges and user-defined functions were removed to simplify the parser. Some of the reserved words (keywords) were renamed so that they all start with a unique first letter. This allows users to type in programs using one-character statements, further reducing memory needs. This was an important consideration on the PDP-8, which was often limited to a few kilobytes (KB).

Like JOSS, and later BASICs, FOCAL on the PDP-8 was a complete environment that included a line editor, an interpreter, and input/output routines. The package as a whole was named FOCAL-8, which also ran on the PDP-5 and PDP-12. When ported to the PDP-11, the resulting FOCAL-11 relied on the underlying operating system, RT-11, to provide file support and editing. The language definition was updated twice, to FOCAL-69 and a very slightly modified FOCAL-71. A port to the Intel 8080 was also available.

FOCAL is notable as the language in which the original versions of the early video games Hamurabi and Lunar Lander were written. Both were later ported to BASIC, where they became much better known.^[3] FOCAL was not popular outside the PDP platform and largely disappeared during the move to the VAX-11. It had a strong revival in the Soviet Union where PDP-11 clones were used as educational and home computers (BK series).