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ALGOL 68RS from RSRE was a portable compiler system written in ALGOL 68RS (bootstrapped from ALGOL 68R), and implemented on a variety of systems including the ICL 2900/Series 39, Multics and 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.
ALGOL 68RS allow the programmer the ability of creating modules, these can be used by other programs and also allowed separate compilation.
Syntax: <lang algol68>PROGRAM [ (holelist ) ] progtitle [ CONTEXT holename IN progtitle ] [ USE uselist ] enclosed clause FINISH</lang> <lang algol68>DECS dectitle CONTEXT holename IN progtitle [ USE uselist ] decsbody KEEP keeplist FINISH</lang>
PROGRAM (thinking, displaying) chess BEGIN MODE PIECE = STRUCT(...); PIECE pieces; ... HERE thinking(PIECE, pieces, BOARD, game); ... HERE displaying(PIECE, pieces, BOARD, game); ... END</lang> <lang algol68>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: <lang algol68>PROGRAM abc COMPOSE game(thinking=thinkmodule, displaying=displayingmodule(piece=displaypiece)) FINISH</lang>