:- module(pio,
	[ phrase_from_file/2,      % :Grammarbody, +File
	  phrase_from_file/3,      % :Grammarbody, +File, +Options
	  phrase_of_from_file/4,   % :Grammarbody, :Reader, +File, +Options
	  rider_to_lazy_list/3,    % :Reader(Stream, Xs0,Xs),Stream, -LazyList
	  stream_to_lazy_list/2,   % :Stream, -LazyList % SWI compatibility
	  run/0
	]).

/** <module> Pure, phrase based, Prolog I/O

This library provides side effect free I/O.  Files can now be
processed in a pure side effect free manner with DCGs.  Many Prolog
predicates only read data from a file, those programs can be made side
effect free.

@author Ulrich Neumerkel
*/


:- use_module(library(error)).

%%	phrase_from_file(:Grammar, +File) is nondet.
%
%	==
%	... --> [] | [_], ... .
%	?- phrase_from_file((..., "searchstring", ...), myfile).

:- op(950,fy, [$]).
$(X) :-
	  copy_term_nat(X,Y),numbervars(Y,0,_),portray_clause(call:Y),
	  X,
	  copy_term_nat(X,Z),numbervars(Z,0,_),portray_clause(exit:Z).
%$(X) :-
%	  copy_term_nat(X,Y),numbervars(Y,0,_),portray_clause(fail:Y),
%	  fail.


:- meta_predicate phrase_from_file(:,+).
:- meta_predicate phrase_from_file(:,+,+).  % debatable

:- meta_predicate phrase_of_from_file(:,:,+,+).

:- load_foreign_files([plstream], [], initIO).

%run :- phrase_of_from_file("a",swi_read_pending_input,a,[]).
run :- 
    setup_call_cleanup(
	$swi_open(a,read,Stream),
		( $rider_to_lazy_list(swi_read_pending_input,Stream,Xs), Xs = "a" ),
	$swi_close(Stream)).
    

phrase_from_file(Nonterminal, File) :-
	phrase_from_file(Nonterminal, File, []).

phrase_from_file(Nonterminal, File, Options) :-
	phrase_of_from_file(Nonterminal, swi_read_pending_input, File, Options).

phrase_of_from_file(Nonterminal, Reader, File, Options) :-
	must_be(list, Options),
	must_be(oneof([[]]), Options),
	setup_call_cleanup(
		$swi_open(File, read, Stream),
		( rider_to_lazy_list(Reader,Stream, Xs), phrase(Nonterminal, Xs) ),
		swi_close(Stream)).

%%	stream_to_lazy_list(+Stream, -Xs) is det.
%






stream_to_lazy_list(Stream, Xs) :-
	rider_to_lazy_list(swi_read_pending_input,Stream, Xs).

rider_to_lazy_list(Reader,Stream, Xs) :-
	swi_stream_property(Stream, position(Pos)),
	freeze(Xs, $step(Reader,Stream, Pos, Xs)).

p(_).

step(Reader,Stream, Pos, Xs0) :-
	$swi_set_stream_position(Stream, Pos),
	(   $swi_at_end_of_stream(Stream)
	->  Xs0 = []
	;   %call(Reader,Stream, Xs0,Xs),
	    $phrase(call(Reader,Stream), Xs0, Xs),
	    $rider_to_lazy_list(Reader,Stream, Xs)
	).


tokenwise(Method,Stream) -->
	[Token],
	{call(Method, Stream, Token)}.