IMPLEMENTATION MODULE StdChans;
(* The standard channels are IOChan's; the "current" channels are
   settable, defaulting to the standards.  NullChan is a closed
   channel (all operations are safe no-ops). *)

IMPORT IOChan;

VAR
  inChan, outChan, errChan : IOChan.ChanId;

PROCEDURE StdInChan () : IOChan.ChanId;
BEGIN RETURN IOChan.StdInChan() END StdInChan;
PROCEDURE StdOutChan () : IOChan.ChanId;
BEGIN RETURN IOChan.StdOutChan() END StdOutChan;
PROCEDURE StdErrChan () : IOChan.ChanId;
BEGIN RETURN IOChan.StdErrChan() END StdErrChan;

PROCEDURE NullChan () : IOChan.ChanId;
BEGIN RETURN IOChan.MakeChan(NIL) END NullChan;

PROCEDURE InChan () : IOChan.ChanId;
BEGIN RETURN inChan END InChan;
PROCEDURE OutChan () : IOChan.ChanId;
BEGIN RETURN outChan END OutChan;
PROCEDURE ErrChan () : IOChan.ChanId;
BEGIN RETURN errChan END ErrChan;

PROCEDURE SetInChan (cid : IOChan.ChanId);
BEGIN inChan := cid END SetInChan;
PROCEDURE SetOutChan (cid : IOChan.ChanId);
BEGIN outChan := cid END SetOutChan;
PROCEDURE SetErrChan (cid : IOChan.ChanId);
BEGIN errChan := cid END SetErrChan;

BEGIN
  inChan := IOChan.StdInChan();
  outChan := IOChan.StdOutChan();
  errChan := IOChan.StdErrChan()
END StdChans.