152 lines
4.0 KiB
Plaintext
152 lines
4.0 KiB
Plaintext
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(* Version 1.10, Nov 1984 *)
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DEFINITION MODULE Termbase;
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(*
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Terminal input/output with redirection hooks
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[Private module of the Modula-2 system]
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Derived from the Lilith Modula-2 system developed by the
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group of Prof. N. Wirth at ETH Zurich, Switzerland.
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*)
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EXPORT QUALIFIED
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ReadProcedure, StatusProcedure, WriteProcedure,
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AssignRead, AssignWrite, UnAssignRead, UnAssignWrite,
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Read, KeyPressed, Write;
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TYPE
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ReadProcedure = PROCEDURE (VAR CHAR);
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(*
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- To assign a private read procedure (for redirection
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of input) a procedure of type 'ReadProcedure' must
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be provided. This procedure returns a character
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from the input device. It waits until a character
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hes been entered.
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*)
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TYPE
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StatusProcedure = PROCEDURE (): BOOLEAN;
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(*
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- To assign a private status-procedure (for redirection
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of input) a procedure of type 'StatusProcedure' must
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be provided. This procedure returns TRUE, if a
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character is available to read, FALSE otherwise.
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*)
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TYPE
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WriteProcedure = PROCEDURE (CHAR);
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(*
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- To assign a private write procedure (for redirection
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of output) a procedure of type 'WriteProcedure' must
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be provided. This is typically used to redirect
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output to a file or to the screen and a file (log
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file). Special interpretation of characters sent to
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the screen can be performed in such a private driver
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procedure.
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*)
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PROCEDURE AssignRead (rp: ReadProcedure;
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sp: StatusProcedure;
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VAR done: BOOLEAN);
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(*
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- Install read and status routines for terminal input.
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in: rp read-a-character procedure,
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sp is-character-available function,
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out: done TRUE if the installation was done.
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Initially the corresponding procedures of 'Keyboard' are
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installed.
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Subsequent assignments will be valid until the next
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'UnAssignRead' is executed or until the (sub-)program
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which has installed the procedures terminates. Upon
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termination of a program, the read and status procedures
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allocated by that program are removed. Read procedures
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are non-sharable resources (see module 'Program').
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The assignments are implemented in a stack manner. When a
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read procedure is removed, the previously valid procedure
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becomes valid again. Up to six levels of re-assignment are
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allowed. Done = FALSE if this depth is exceeded.
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During execution of a read or status procedure, this
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assignments-stack is decremented, which allows an
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installed routine to call recursively Terminal.Read
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and/or Terminal.KeyPressed to activate the previously
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installed routine. At the lowest level however, the
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stack is not decremented.
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*)
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PROCEDURE AssignWrite (wp: WriteProcedure;
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VAR done: BOOLEAN);
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(*
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- Install write routine for terminal output.
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in: wp character output procedure,
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out: done set TRUE if the installation was done.
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[See AssignRead above.]
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Initially the procedure Display.Write is assigned.
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*)
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PROCEDURE UnAssignRead (VAR done: BOOLEAN);
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(*
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- Undo the last AssignRead by the current program.
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out: done set TRUE if there was something to unassign.
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The previously valid procedures become active again.
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*)
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PROCEDURE UnAssignWrite (VAR done: BOOLEAN);
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(*
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- Undo the last AssignWrite by the current program.
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out: done set TRUE if there was something to unassign.
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The previously valid procedure becomes active again.
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*)
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PROCEDURE Read (VAR ch: CHAR);
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(*
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- Read a character using the current input procedure.
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out: ch the character read.
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Uses the current read-procedure, as assigned by
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AssignRead.
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*)
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PROCEDURE KeyPressed (): BOOLEAN;
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(*
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- Test if a character is available from the current input.
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Uses the current status-procedure, as assigned by
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AssignRead.
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*)
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PROCEDURE Write (ch: CHAR);
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(*
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- Write a character to the current output.
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in: ch character to write.
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Uses the current write-procedure as assigned by
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AssignWrite.
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*)
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END Termbase.
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