DEFINITION MODULE IOChan;
(* A minimal channel abstraction over the runtime streams (an
   ISO-style ChanId).  ChanId is opaque; the standard channels are
   the standard input/output/error streams. *)

TYPE ChanId;

PROCEDURE StdInChan() : ChanId;
PROCEDURE StdOutChan() : ChanId;
PROCEDURE StdErrChan() : ChanId;

PROCEDURE ReadChar(cid : ChanId) : CHAR;
PROCEDURE WriteChar(cid : ChanId; c : CHAR);
PROCEDURE WriteString(cid : ChanId; VAR s : ARRAY OF CHAR);
PROCEDURE WriteLn(cid : ChanId);
PROCEDURE WriteInt(cid : ChanId; n : INTEGER);

END IOChan.