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    1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2015, VU University Amsterdam
    7    All rights reserved.
    8
    9    Redistribution and use in source and binary forms, with or without
   10    modification, are permitted provided that the following conditions
   11    are met:
   12
   13    1. Redistributions of source code must retain the above copyright
   14       notice, this list of conditions and the following disclaimer.
   15
   16    2. Redistributions in binary form must reproduce the above copyright
   17       notice, this list of conditions and the following disclaimer in
   18       the documentation and/or other materials provided with the
   19       distribution.
   20
   21    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   22    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   23    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   24    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   25    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   26    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   27    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   28    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   29    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   31    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   32    POSSIBILITY OF SUCH DAMAGE.
   33*/
   34
   35:- module(prolog_stream,
   36          [ open_prolog_stream/4        % +Module, +Mode, -Stream, +Data
   37          ]).   38:- use_foreign_library(foreign(prolog_stream)).

A stream with Prolog callbacks

This library defines a Prolog stream that realises its low-level I/O with callbacks to Prolog. The library was developed to bind normal Prolog I/O to Pengines I/O. This type of I/O redirection is probably the primary use case. */

 open_prolog_stream(+Module, +Mode, -Stream, +Options)
Create a new stream that implements its I/O by calling predicates in Module. The called predicates are:
Module:+Stream:+String
Called for a Mode = write stream if data is available. String contains the (textual) data that is written to Stream. The callback is called if the buffer of Stream overflows, the user calls flush_output(Stream) or Stream is closed and there is buffered data.
Module:+Stream:-Term
Called for a Mode == read stream to get new data. On success the stream extracts text from the provided Term. Term is typically a string, atom, code or character list. If term is not one of the above, it is handed to writeq/1. To signal end-of-file, unify stream with an empty text, e.g., stream_read(Stream, "").
Module:stream_close(+Stream)
Called when the stream is closed. This predicate must succeed. The callback can be used to cleanup associated resources.

The current implementation only deals with text streams. The stream uses the wchar_t encoding. The buffer size must be a multiple of wchar_t, i.e., a multiple of four for portability. The newline mode of the stream is posix on all platforms, disabling the translation "\n" --> "\r\n".

Arguments:
Options- is currently ignored.
bug
- Futher versions might require additional callbacks. As we demand all callbacks to be defined, existing code needs to implement the new callbacks.