Merge pull request #596 from triska/sgml

ADDED: library(sgml), providing load_html/3 to parse HTML documents

src/lib/sgml.pl

@@ -0,0 +1,41 @@
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Predicates for parsing markup documents.
+   Written June 2020 by Markus Triska (triska@metalevel.at)
+   Part of Scryer Prolog.
+
+   Currently, only a single predicate is provided:
+
+   load_html(+In, -Es, +Options)
+   =============================
+
+   In must be a stream, specified as stream(S), and Es is unified with
+   a list of elements of the form:
+
+   * a list of characters, representing text
+
+   * element(Name, Attrs, Children)
+     - Name is the name of the tag
+     - Attrs is a list of Key=Value pairs:
+       Key is an atom, and Value is a list of characters
+     - Children is a list of elements as specified here.
+
+   Currently, Options are ignored. In the future, more options may be
+   provided to control parsing.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+:- module(sgml, [load_html/3]).
+
+:- use_module(library(iso_ext)).
+:- use_module(library(error)).
+
+load_html(stream(Stream), [E], Options) :-
+        must_be(list, Options),
+        read_to_end(Stream, Cs),
+        '$load_html'(Cs, E, []).
+
+read_to_end(Stream, Cs) :-
+        '$get_n_chars'(Stream, 4096, Cs0),
+        (   Cs0 = [] -> Cs = []
+        ;   partial_string(Cs0, Cs, Rest),
+            read_to_end(Stream, Rest)
+        ).