DEFINITION MODULE StdChans;

  (* Access to standard and default channels *)

IMPORT IOChan;

TYPE
  ChanId = IOChan.ChanId;
    (* Values of this type are used to identify channels *)

  (* The following functions return the standard channel values.
     These channels cannot be closed.
  *)

PROCEDURE StdInChan (): ChanId;
  (* Returns the identity of the implementation-defined standard source for
program
     input.
  *)

PROCEDURE StdOutChan (): ChanId;
  (* Returns the identity of the implementation-defined standard source for program
     output.
  *)

PROCEDURE StdErrChan (): ChanId;
  (* Returns the identity of the implementation-defined standard destination for program
     error messages.
  *)

PROCEDURE NullChan (): ChanId;
  (* Returns the identity of a channel open to the null device. *)

  (* The following functions return the default channel values *)

PROCEDURE InChan (): ChanId;
  (* Returns the identity of the current default input channel. *)

PROCEDURE OutChan (): ChanId;
  (* Returns the identity of the current default output channel. *)

PROCEDURE ErrChan (): ChanId;
  (* Returns the identity of the current default error message channel. *)

  (* The following procedures allow for redirection of the default channels *)

PROCEDURE SetInChan (cid: ChanId);
  (* Sets the current default input channel to that identified by cid. *)

PROCEDURE SetOutChan (cid: ChanId);
  (* Sets the current default output channel to that identified by cid. *)

PROCEDURE SetErrChan (cid: ChanId);
  (* Sets the current default error channel to that identified by cid. *)

END StdChans.

