{{wikipedia}}{{implementation|ALGOL 68}} ALGOL 68RS from [[wp:Royal_Signals_and_Radar_Establishment|RSRE]] was a portable compiler system written in ALGOL 68RS (bootstrapped from [[ALGOL 68R]]), and implemented on a variety of systems including the [[wp:wiki_ICL_2900_Series|ICL 2900]]/[[wp:ICL_Series_39|Series 39]], [[Multics]] and [[wp:VAX|DEC VAX/VMS]].

The language was based on the Revised Report, but with similar subset restrictions to [[ALGOL 68R]]. This compiler survives in the form of an Algol68-to-C compiler aka [[ELLA ALGOL 68]].

== Modules == ''ALGOL 68RS'' allow the programmer the ability of creating ''modules'', these can be '''use'''d by other programs and also allowed separate compilation.

Syntax:

PROGRAM [ (holelist ) ] progtitle
[ CONTEXT holename IN progtitle ]
[ USE uselist ]
enclosed clause
FINISH

DECS dectitle
CONTEXT holename IN progtitle
[ USE uselist ]
decsbody
KEEP keeplist
FINISH

Example

PROGRAM (thinking, displaying) chess
BEGIN
  MODE PIECE = STRUCT(...);
  [12]PIECE pieces;
  ...
  HERE thinking(PIECE, pieces, BOARD, game);
  ...
  HERE displaying(PIECE, pieces, BOARD, game);
  ...
END

PROGRAM thinkmodule
CONTEXT thinking IN chess
...
FINISH

An entire program can thus be '''composed''' of pieces of other modules, particularly if a ''hole'' contains a sub-''hole'' (eg displaypiece), then this ''hole'' can in-turn be pulled into the composition.

Example:

PROGRAM abc
COMPOSE game(thinking=thinkmodule, displaying=displayingmodule(piece=displaypiece))
FINISH