ALGOL 68RS

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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 VAX/VMS.

The language was based on the Revised Report, but with similar subset restrictions to ALGOL 68R. This compiler survives i/n 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 used 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