strengthen and improve type checks
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Predicates for parsing HTML and XML documents.
- Written June 2020 by Markus Triska (triska@metalevel.at)
+ Written 2020-2022 by Markus Triska (triska@metalevel.at)
Part of Scryer Prolog.
Currently, two predicates are provided:
:- use_module(library(charsio)).
load_html(Source, Es, Options) :-
+ must_be_source(Source, load_html/3),
+ must_be(list, Options),
load_structure_(Source, Es, Options, html).
load_xml(Source, Es, Options) :-
+ must_be_source(Source, load_xml/3),
+ must_be(list, Options),
load_structure_(Source, Es, Options, xml).
+must_be_source(Source, Context) :-
+ ( var(Source) -> instantiation_error(Context)
+ ; is_sgml_source(Source) -> true
+ ; domain_error(sgml_source, Source, Context)
+ ).
+
+is_sgml_source(file(Fs)) :- must_be(chars, Fs).
+is_sgml_source(stream(_)).
+is_sgml_source([]).
+is_sgml_source([C|Cs]) :- must_be(chars, [C|Cs]).
+
load_structure_([], [], _, _).
load_structure_([C|Cs], [E], Options, What) :-
load_(What, [C|Cs], E, Options).
load_structure_(file(Fs), [E], Options, What) :-
- must_be(list, Options),
- must_be(chars, Fs),
once(phrase_from_file(seq(Cs), Fs)),
load_(What, Cs, E, Options).
load_structure_(stream(Stream), [E], Options, What) :-
- must_be(list, Options),
get_n_chars(Stream, _, Cs),
load_(What, Cs, E, Options).
