ADDED: phrase_to_stream/2, writing a list of characters to a stream.

src/lib/pio.pl

@@ -1,17 +1,19 @@
 :- 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)).