/* Part of SWI-Prolog
Author: Jan Wielemaker
Copyright (c) 2015, VU University Amsterdam
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[ open_prolog_stream/4 % +Module, +Mode, -Stream, +Data
/** <module> 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_write(+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_read(+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
% 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"`.
% @arg 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.