M2compiler-V3/docs/wip/streamfile.mod

IMPLEMENTATION MODULE StreamFile;
(* Open/close maps onto IOChan's OpenRead/OpenWrite; IsStreamFile is
   TRUE for any open channel (V3's channels are all streams). *)

IMPORT IOChan, ChanConsts;
FROM ChanConsts IMPORT opened, noSuchFile, wrongFlags;
FROM ChanConsts IMPORT readFlag, writeFlag;

PROCEDURE HasFlag (flags : ChanConsts.FlagSet;
                   f : ChanConsts.ChanFlags) : BOOLEAN;
BEGIN
  RETURN f IN flags
END HasFlag;

PROCEDURE Open (VAR cid : IOChan.ChanId; name : ARRAY OF CHAR;
                flags : ChanConsts.FlagSet;
                VAR res : ChanConsts.OpenResults);
  VAR c : IOChan.ChanId;
BEGIN
  c := IOChan.MakeChan(NIL);
  IF HasFlag(flags, readFlag) THEN
    (* read implies old *)
    IF NOT IOChan.IsOpen(IOChan.OpenRead(name)) THEN
      cid := c; res := noSuchFile; RETURN
    END;
    c := IOChan.OpenRead(name)
  ELSIF HasFlag(flags, writeFlag) THEN
    c := IOChan.OpenWrite(name);
    IF NOT IOChan.IsOpen(c) THEN
      cid := IOChan.MakeChan(NIL); res := noSuchFile; RETURN
    END
  ELSE
    cid := c; res := wrongFlags; RETURN
  END;
  cid := c;
  res := opened
END Open;

PROCEDURE IsStreamFile (cid : IOChan.ChanId) : BOOLEAN;
BEGIN
  RETURN IOChan.IsOpen(cid)
END IsStreamFile;

PROCEDURE Close (VAR cid : IOChan.ChanId);
BEGIN
  IOChan.Close(cid)
END Close;

END StreamFile.