ADDED: Rudimentary version of phrase_to_file/2 in library(pio)
See for more information.
:- module(pio, [phrase_from_file/2,
- phrase_from_file/3]).
+ phrase_from_file/3,
+ phrase_to_file/2]).
:- use_module(library(dcgs)).
:- use_module(library(error)).
:- use_module(library(freeze)).
:- use_module(library(iso_ext), [setup_call_cleanup/3, partial_string/3]).
:- use_module(library(lists), [member/2]).
+:- use_module(library(format), [format/3]).
:- meta_predicate phrase_from_file(2, ?).
:- meta_predicate phrase_from_file(2, ?, ?).
+:- meta_predicate phrase_to_file(2, ?).
phrase_from_file(NT, File) :-
phrase_from_file(NT, File, []).
@@ -43,3 +46,29 @@ reader_step(Stream, Pos, Xs0) :-
partial_string(Cs, Xs0, Xs),
stream_to_lazy_list(Stream, Xs)
).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+ phrase_to_file(+GRBody, +File)
+
+ Emit the list of characters described by the grammar rule body
+ GRBody to File. File is a string, which is also the representation
+ used by library(files) to test for existence etc. of files.
+
+ An ideal implementation of phrase_to_file/2 writes each character
+ as soon as it becomes known and no choice-points remain, and thus
+ avoids the manifestation of the entire string in memory. See #691
+ for more information.
+
+ The current preliminary implementation is provided so that Prolog
+ programmers can already get used to describing output with DCGs,
+ and then writing it to a file when necessary. This simple
+ implementation suffices as long as the entire contents can be
+ represented in memory, and thus covers a large number of use cases.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+phrase_to_file(GRBody, File) :-
+ atom_chars(Atom, File),
+ phrase(GRBody, Chars),
+ setup_call_cleanup(open(Atom, write, Stream),
+ format(Stream, "~s", [Chars]),
+ close(Stream)).
