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  (* Independent sequential data streams *)
IMPORT IOChan, ChanConsts;
  ChanId = IOChan.ChanId;
  FlagSet = ChanConsts.FlagSet;
  OpenResults = ChanConsts.OpenResults;
  (* Accepted singleton values of FlagSet *)
  read = FlagSet{ChanConsts.readFlag};   (* input operations are requested/available *)
  write = FlagSet{ChanConsts.writeFlag}; (* output operations are requested/available *)
  old = FlagSet{ChanConsts.oldFlag};     (* a file may/must/did exist before the channel is
                                            opened *)
  text = FlagSet{ChanConsts.textFlag};   (* text operations are requested/available *)
  raw = FlagSet{ChanConsts.rawFlag};     (* raw operations are requested/available *)
PROCEDURE Open (VAR cid: ChanId; name: ARRAY OF CHAR; flags: FlagSet; VAR res: OpenResults);
  (* Attempts to obtain and open a channel connected to a sequential stream of the given name.
     Without the write flag, read is implied; the read flag implies old;
     without the raw flag, text is implied.
     If successful, assigns to cid the identity of the opened channel, and assigns the value
     opened to res.
     If a channel cannot be opened as required, the value of res indicates the reason, and
     cid identifies the invalid channel.
PROCEDURE IsStreamFile (cid: ChanId): BOOLEAN;
  (* Tests if the channel identified by cid is open to a sequential stream. *)
PROCEDURE Close (VAR cid: ChanId);
  (* If the channel identified by cid is not open to a sequential stream, the exception
     wrongDevice is raised; otherwise closes the channel, and assigns the value identifying
     the invalid channel to cid.
END StreamFile.