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_module(library(shlib)).
  39:- use_foreign_library(foreign(prolog_stream)).
  40
  41/** <module> A stream with Prolog callbacks
  42
  43This library defines a Prolog  stream   that  realises its low-level I/O
  44with callbacks to Prolog.  The  library   was  developed  to bind normal
  45Prolog I/O to Pengines I/O. This type of I/O redirection is probably the
  46primary use case.
  47*/
  48
  49%!  open_prolog_stream(+Module, +Mode, -Stream, +Options)
  50%
  51%   Create  a  new  stream  that  implements   its  I/O  by  calling
  52%   predicates in Module.  The called predicates are:
  53%
  54%     - Module:stream_write(+Stream, +String)
  55%     Called for a `Mode = write` stream if data is available.
  56%     String contains the (textual) data that is written
  57%     to Stream.  The callback is called if the buffer of
  58%     Stream overflows, the user calls flush_output(Stream)
  59%     or Stream is closed and there is buffered data.
  60%     - Module:stream_read(+Stream, -Term)
  61%     Called for a `Mode == read` stream to get new data.  On
  62%     success the stream extracts text from the provided Term.
  63%     Term is typically a string, atom, code or character list.
  64%     If term is not one of the above, it is handed to writeq/1.
  65%     To signal end-of-file, unify stream with an empty text,
  66%     e.g., `stream_read(Stream, "")`.
  67%     - Module:stream_close(+Stream)
  68%     Called when the stream is closed.  This predicate must
  69%     succeed.  The callback can be used to cleanup associated
  70%     resources.
  71%
  72%   The current implementation only  deals   with  text streams. The
  73%   stream uses the =wchar_t= encoding. The   buffer  size must be a
  74%   multiple of =wchar_t=, i.e., a multiple of four for portability.
  75%   The _newline_ mode of the stream   is  =posix= on all platforms,
  76%   disabling the translation `"\n" --> "\r\n"`.
  77%
  78%   @arg Options is currently ignored.
  79%   @bug    Futher versions might require additional callbacks.  As we
  80%           demand all callbacks to be defined, existing code needs
  81%           to implement the new callbacks.