ADDED: phrase_to_stream/2, writing a list of characters to a stream.
:- module(pio, [phrase_from_file/2,
phrase_from_file/3,
- phrase_to_file/2]).
+ phrase_to_file/2,
+ phrase_to_stream/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]).
+:- use_module(library(iso_ext), [setup_call_cleanup/3, partial_string/1, partial_string/3]).
+:- use_module(library(lists), [member/2, maplist/2]).
:- meta_predicate(phrase_from_file(2, ?)).
:- meta_predicate(phrase_from_file(2, ?, ?)).
:- meta_predicate(phrase_to_file(2, ?)).
+:- meta_predicate(phrase_to_stream(2, ?)).
phrase_from_file(NT, File) :-
phrase_from_file(NT, File, []).
@@ -46,13 +48,12 @@ reader_step(Stream, Pos, Xs0) :-
).
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- phrase_to_file(+GRBody, +File)
+ phrase_to_stream(+GRBody, +Stream)
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.
+ GRBody to Stream.
- An ideal implementation of phrase_to_file/2 writes each character
+ An ideal implementation of phrase_to_stream/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.
@@ -64,9 +65,31 @@ reader_step(Stream, Pos, Xs0) :-
represented in memory, and thus covers a large number of use cases.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+phrase_to_stream(GRBody, Stream) :-
+ phrase(GRBody, Cs),
+ ( partial_string(Cs) -> % very efficiently check for a string
+ true % (success is the expected case here)
+ ; must_be(list, Cs),
+ maplist(must_be(character), Cs)
+ ),
+ ( stream_property(Stream, type(binary)) ->
+ ( '$first_non_octet'(Cs, N) ->
+ domain_error(byte_char, N, phrase_to_stream/2)
+ ; true
+ )
+ ; true
+ ),
+ % we use a specialised internal predicate that uses only a
+ % single "write" operation for efficiency. It is equivalent to
+ % maplist(put_char(Stream), Cs). It also works for binary streams.
+ '$put_chars'(Stream, Cs).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+ phrase_to_file(+GRBody, +File), writing the string described
+ by GRBody to File.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
phrase_to_file(GRBody, File) :-
- atom_chars(Atom, File),
- phrase(GRBody, Chars),
- setup_call_cleanup(open(Atom, write, Stream),
- format(Stream, "~s", [Chars]),
+ setup_call_cleanup(open(File, write, Stream),
+ phrase_to_stream(GRBody, Stream),
close(Stream)).
