3.20.5 Examples for using the HTML write library

In the following example we will generate a table of Prolog predicates we find from the SWI-Prolog help system based on a keyword. The primary database is defined by the predicate predicate/5 We will make hyperlinks for the predicates pointing to their documentation.

html_apropos(Kwd) :-
        findall(Pred, apropos_predicate(Kwd, Pred), Matches),
        phrase(apropos_page(Kwd, Matches), Tokens),
        print_html(Tokens).

%       emit page with title, header and table of matches

apropos_page(Kwd, Matches) -->
        page([ title(['Predicates for ', Kwd])
             ],
             [ h2(align(center),
                  ['Predicates for ', Kwd]),
               table([ align(center),
                       border(1),
                       width('80%')
                     ],
                     [ tr([ th('Predicate'),
                            th('Summary')
                          ])
                     | \apropos_rows(Matches)
                     ])
             ]).

%       emit the rows for the body of the table.

apropos_rows([]) -->
        [].
apropos_rows([pred(Name, Arity, Summary)|T]) -->
        html([ tr([ td(\predref(Name/Arity)),
                    td(em(Summary))
                  ])
             ]),
        apropos_rows(T).

%       predref(Name/Arity)
%
%       Emit Name/Arity as a hyperlink to
%
%               /cgi-bin/plman?name=Name&arity=Arity
%
%       we must do form-encoding for the name as it may contain illegal
%       characters.  www_form_encode/2 is defined in library(url).

predref(Name/Arity) -->
        { www_form_encode(Name, Encoded),
          sformat(Href, '/cgi-bin/plman?name=~w&arity=~w',
                  [Encoded, Arity])
        },
        html(a(href(Href), [Name, /, Arity])).

%       Find predicates from a keyword. '$apropos_match' is an internal
%       undocumented predicate.

apropos_predicate(Pattern, pred(Name, Arity, Summary)) :-
        predicate(Name, Arity, Summary, _, _),
        (   '$apropos_match'(Pattern, Name)
        ->  true
        ;   '$apropos_match'(Pattern, Summary)
        ).