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(* StdIO.mod provides general Read and Write procedures.
Copyright (C) 2001-2024 Free Software Foundation, Inc.
Contributed by Gaius Mulley <gaius.mulley@southwales.ac.uk>.
This file is part of GNU Modula-2.
GNU Modula-2 is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
GNU Modula-2 is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<http://www.gnu.org/licenses/>. *)
IMPLEMENTATION MODULE StdIO ;
IMPORT IO ;
CONST
MaxStack = 40 ;
VAR
StackW : ARRAY [0..MaxStack] OF ProcWrite ;
StackWPtr: CARDINAL ;
StackR : ARRAY [0..MaxStack] OF ProcRead ;
StackRPtr: CARDINAL ;
(*
Read - is the generic procedure that all higher application layers
should use to receive a character.
*)
PROCEDURE Read (VAR ch: CHAR) ;
BEGIN
StackR[StackRPtr](ch)
END Read ;
(*
Write - is the generic procedure that all higher application layers
should use to emit a character.
*)
PROCEDURE Write (ch: CHAR) ;
BEGIN
StackW[StackWPtr](ch)
END Write ;
(*
PushOutput - pushes the current Write procedure onto a stack,
any future references to Write will actually invoke
procedure, p.
*)
PROCEDURE PushOutput (p: ProcWrite) ;
BEGIN
IF StackWPtr=MaxStack
THEN
HALT
ELSE
INC(StackWPtr) ;
StackW[StackWPtr] := p
END
END PushOutput ;
(*
PopOutput - restores Write to use the previous output procedure.
*)
PROCEDURE PopOutput ;
BEGIN
IF StackWPtr=1
THEN
HALT
ELSE
DEC(StackWPtr)
END
END PopOutput ;
(*
GetCurrentOutput - returns the current output procedure.
*)
PROCEDURE GetCurrentOutput () : ProcWrite ;
BEGIN
IF StackWPtr>0
THEN
RETURN( StackW[StackWPtr] )
ELSE
HALT
END
END GetCurrentOutput ;
(*
PushInput - pushes the current Read procedure onto a stack,
any future references to Read will actually invoke
procedure, p.
*)
PROCEDURE PushInput (p: ProcRead) ;
BEGIN
IF StackRPtr=MaxStack
THEN
HALT
ELSE
INC(StackRPtr) ;
StackR[StackRPtr] := p
END
END PushInput ;
(*
PopInput - restores Write to use the previous output procedure.
*)
PROCEDURE PopInput ;
BEGIN
IF StackRPtr=1
THEN
HALT
ELSE
DEC(StackRPtr)
END
END PopInput ;
(*
GetCurrentInput - returns the current input procedure.
*)
PROCEDURE GetCurrentInput () : ProcRead ;
BEGIN
IF StackRPtr>0
THEN
RETURN( StackR[StackRPtr] )
ELSE
HALT
END
END GetCurrentInput ;
BEGIN
StackWPtr := 0 ;
StackRPtr := 0 ;
PushOutput(IO.Write) ;
PushInput(IO.Read)
END StdIO.
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