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iochan.def
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1996-08-29
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DEFINITION MODULE IOChan;
(* Types and procedures forming the interface to channels for
device-independent data transfer modules *)
FROM ChanConsts IMPORT FlagSet;
FROM IOConsts IMPORT ReadResults;
FROM SYSTEM IMPORT ADDRESS;
TYPE
ChanId; (* Values of this type are used to identify channels *)
(* There is one pre-defined value identifying a bad channel on which no
data transfer operations are available. It is used to initialize
variables of type ChanId: *)
PROCEDURE InvalidChan () : ChanId;
(* Returns the value identifying the bad channel *)
(* For each of the following operations, if the device supports the
operation on the channel, the behaviour of the procedure conforms with the
description below. The full behaviour is defined for each device module.
If the device does not support the operation on the channel, the behaviour
of the procedure is to raise the exception notAvailable. *)
(* Text operations - these perform any required translation between
the internal and external representation of text. *)
PROCEDURE Look ( cid : ChanId;
VAR ch : CHAR;
VAR res : ReadResults);
(* If there is a character as the next item in the given input stream,
assigns its value to the parameter ch without removing it from the stream.
Otherwise, the value of the parameter ch is not defined.
The parameter res, and the stored read result, is set to the value
allRight, endOfLine, or endOfInput. *)
PROCEDURE Skip (cid : ChanId);
(* If the input has ended, the exception skipAtEnd is raised,
otherwise, the next character or line mark in the input is removed
and the stored read result is set to the value allRight. *)
PROCEDURE SkipLook ( cid : ChanId;
VAR ch : CHAR;
VAR res : ReadResults);
(* If the stream has ended, the exception skipAtEnd is raised,
otherwise, the next character or line mark is removed.
If there is a character as the next item in the given input stream,
assignsd its value to the parameter ch without removing it from the stream.
Otherwise, the value of the parameter ch is not defined.
The parameter res, and the stored read result, is set to the value
allRight, endOfLine or endOfInput. *)
PROCEDURE WriteLn (cid : ChanId);
(* Writes a line mark over the channel *)
PROCEDURE TextRead ( cid : ChanId;
to : ADDRESS;
maxChars : CARDINAL;
VAR charsRead : CARDINAL);
(* Reads at most maxChars characters from the current line and assigns
corresponding values to successive locations, starting at the address
given by the parameter to, and continuing at increments corresponding
to the address difference between successive components of an ARRAY OF
CHAR. The number of characters read is assigned to the parameter charsRead.
The read result is set to the value allRight, endOfLine, or endOfInput. *)
PROCEDURE TextWrite (cid : ChanId;
from : ADDRESS;
charsToWrite : CARDINAL);
(* Writes a number of characters given by the value of the parameter
charsToWrite,
starting as the address given by the parameter from and continuing at
increments corresponding to the address difference between successive
components of an ARRAY OF CHAR. *)
(* Raw operations *)
PROCEDURE RawRead ( cid : ChanId;
to : ADDRESS;
maxLocs : CARDINAL;
VAR locsRead : CARDINAL);
(* Reads at most maxLocs items and assigns corresponding values to
successive locations, starting at the address given by the parameter to.
The number of items read is assigned to the parameter locsRead.
The read result is set to the value allRight or endOfInput. *)
PROCEDURE RawWrite (cid : ChanId;
from : ADDRESS;
locsToWrite : CARDINAL);
(* Writes a number of items given by the value of the parameter locsToWrite from
successive locations starting as the address given by the parameter from. *)
(* Common operations *)
PROCEDURE GetName ( cid : ChanId;
VAR s : ARRAY OF CHAR);
(* Copies to the parameter s a name associated with the channel,
possibly truncated depending on the capacity of s. *)
PROCEDURE Reset (cid : ChanId);
(* Reset to a state defined by the device module *)
PROCEDURE Flush (cid : ChanId);
(* Flush any data buffered by the device module out to the destination *)
(* Access to read results *)
PROCEDURE SetReadResult (cid : ChanId;
res : ReadResults);
(* Sets the read result value for the channel to the value res *)
PROCEDURE ReadResult (cid : ChanId) : ReadResults;
(* Returns the stored read result value for the channel *)
(* (This is initially the value notKnown) *)
(* Users can discover which flags actually apply to a channel *)
PROCEDURE CurrentFlags (cid : ChanId) : FlagSet;
(* Returns the set of flags that apply to the given channel *)
(* The following exceptions are defined for this module and its clients *)
TYPE
ChanExceptions = (
ChanNoException, (* there is no exception in this context *)
notChanException,(* there is an exception in this context, from another source *)
wrongDevice, (* device specific operations on wrong device *)
notAvailable, (* operation attempted that is not available on that channel *)
skipAtEnd, (* attempt to skip data from a stream that has ended *)
softDeviceError, (* device specific recoverable error *)
hardDeviceError, (* device specific non-recoverable error *)
textParseError, (* input data does not correspond to a character or line mark
- optional detection *)
notAChannel (* given value does not identify a channel
- optional detection *)
);
PROCEDURE IsChanException (): BOOLEAN;
(* Returns TRUE if the current coroutine is in the exceptional execution state
because of the raising of an exception from ChanExceptions*)
PROCEDURE ChanException (): ChanExceptions;
(* If the current coroutine is in the exceptional execution state because of
the raising of an exception from ChanExceptions, returns the corresponding
enumeration value, and otherwise raises an exception *)
(* When a device procedure detects a device error, it raises the exception
softDeviceError or hardDeviceError. If these exceptions are handled, the
following procedure may be used to discover an implementation-defined error
number for the channel. *)
TYPE
DeviceErrNum = INTEGER;
PROCEDURE DeviceError (cid : ChanId): DeviceErrNum;
(* If a device error exception has been raised, returns the error
number stored by the device module. *)
END IOChan.