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- DEFINITION MODULE IOChan;
- (* A channel abstraction over the runtime streams and files (an
- ISO-style ChanId). ChanId is opaque: the standard channels wrap
- stdio streams, and OpenRead/OpenWrite wrap a file. A failed open
- returns a closed channel (IsOpen = FALSE); operations on a closed
- channel are safe no-ops (ReadChar returns 0C). *)
- FROM SYSTEM IMPORT ADDRESS;
- TYPE ChanId;
- (* --- standard channels --- *)
- PROCEDURE StdInChan() : ChanId;
- PROCEDURE StdOutChan() : ChanId;
- PROCEDURE StdErrChan() : ChanId;
- (* --- file channels --- *)
- PROCEDURE OpenRead(VAR name : ARRAY OF CHAR) : ChanId;
- PROCEDURE OpenWrite(VAR name : ARRAY OF CHAR) : ChanId;
- PROCEDURE Close(VAR cid : ChanId);
- PROCEDURE IsOpen(cid : ChanId) : BOOLEAN;
- (* --- bridging (for libraries layered on channels, e.g. Files) --- *)
- PROCEDURE Handle(cid : ChanId) : ADDRESS;
- (* The underlying runtime handle of cid (NIL for a closed channel). *)
- PROCEDURE MakeChan(h : ADDRESS) : ChanId;
- (* Wraps a runtime handle as a ChanId (NIL yields a closed channel). *)
- (* --- operations --- *)
- PROCEDURE ReadChar(cid : ChanId) : CHAR;
- PROCEDURE ReadString(cid : ChanId; VAR s : ARRAY OF CHAR); (* one line *)
- PROCEDURE ReadInt(cid : ChanId) : INTEGER;
- PROCEDURE WriteChar(cid : ChanId; c : CHAR);
- PROCEDURE WriteString(cid : ChanId; VAR s : ARRAY OF CHAR);
- PROCEDURE WriteInt(cid : ChanId; n : INTEGER);
- PROCEDURE WriteLn(cid : ChanId);
- (* --- positioning (seekable channels) --- *)
- PROCEDURE Position(cid : ChanId) : INTEGER;
- (* Current byte offset (-1 when unknown/closed). *)
- PROCEDURE Seek(cid : ChanId; pos : INTEGER) : BOOLEAN;
- (* Absolute seek; FALSE on failure. *)
- PROCEDURE Rewind(cid : ChanId) : BOOLEAN;
- (* Seek to offset 0. *)
- END IOChan.
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