View source for FOCAL

'''FOCAL''' was an early [[interpreter|interpreted]] [[programming language]], very similar to [[BASIC]], produced by [[Digital Equipment Corporation|DEC]] for use on smaller computers such as the [[PDP-8]].

The [[syntax]] of FOCAL is very similar to that of BASIC; every [[statement]] has a line number. Statements can be entered in any order, but they will be [[execute]]d in numerical order. One difference is that BASIC line numbers are integers, but FOCAL line numbers are in two parts (looking rather like [[floating point]] numbers). This allows groups of lines to be treated as an entity, e.g. for [[subroutine]]s.

[[Conditional]] statements ('IF') include an [[expression]], and three lines numbers. If the expression's value is less than zero, the first statement is executed; if zero, the second; or if greater than zero, the third. The second and third lines numbers are optional. [[Loop]]s ('FOR') are also available.

[[Variable]] names are one or two characters long, of which the first must be a letter (other than 'F'). All variables always have a [[type]] of floating point. [[Array]]s are available.

A [[subroutine package|library]] of trigonometric functions is standard.

{{semi-stub}}

==See also==

* [[Running Lunar Lander on the PDP-8 Using Paper Tape FOCAL]] - an example of a FOCAL program

==External links==

* [http://www.bitsavers.org/pdf/dec/pdp8/focal/ PDP-8 FOCAL] - documentation at [[Bitsavers]]
** [http://www.bitsavers.org/pdf/dec/pdp8/focal/DEC-08-AJAB-D_FOCAL_Programming_Manual_1968.pdf FOCAL Programming Manual] (DEC-08-AJAB-D)
** [http://www.bitsavers.org/pdf/dec/pdp8/focal/A_FOCAL_Primer_2nd_Edition_1972.pdf A FOCAL Primer]
* [http://www.vandermark.ch/pdp8/uploads/PDP8/PDP8.Manuals/Focal-Help.txt DPF FOCAL]

[[Category: Languages]]