html_quasiquotations.pl

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2013-2015, VU University Amsterdam
    All rights reserved.

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*/

:- module(html_quasi_quotations, [ html/4 ]).
:- use_module(library(sgml)).
:- use_module(library(apply)).
:- use_module(library(error)).
:- use_module(library(lists)).
:- use_module(library(quasi_quotations)).

/** <module> HTML quasi quotations

This  module  implements  quasi  quotations   for  HTML.  Together  with
library(http/html_write),  this  allows  for  inclusion   of  long  HTML
fragments in the Prolog  source  code   while  replacing  attributes and
content with variable that come from the surrounding Prolog clause.

This module is included and re-exported from library(http/html_write).

@see    library(http/js_write) provides quasi quotation for JavaScript.
*/

%!  html(+Content, +Vars, +VarDict, -DOM) is det.
%
%   The predicate html/4 implements  HTML   quasi  quotations. These
%   quotations produce a DOM term that   is suitable for html//1 and
%   other predicates that are declared to   consume this format. The
%   quasi quoter only  accepts  valid,   but  possibly  partial HTML
%   documents. The document *must* begin  with   a  tag.  The quoter
%   replaces attributes or content whose value  is a Prolog variable
%   that appears in the argument list   of  the =html= indicator. If
%   the variable defines content, it must  be the only content. Here
%   is  an  example,  replacing  both  a   content  element  and  an
%   attribute. Note that the document is valid HTML.
%
%     ==
%       html({|html(Name, URL)||
%              <p>Dear <span class="name">Name</span>,
%
%              <p>You can <a href="URL">download</a> the requested
%              article now.
%              |}
%     ==

:- quasi_quotation_syntax(html).

html(Content, Vars, Dict, DOM) :-
    must_be(list, Dict),
    include(qq_var(Vars), Dict, QQDict),
    with_quasi_quotation_input(
        Content, In,
        load_html(In, DOM0,
                  [ max_errors(0),
                    syntax_errors(print),
                    case_preserving_attributes(true)
                  ])),
    xml_content(QQDict, DOM0, DOM).

qq_var(Vars, _=Var) :- member(V, Vars), V == Var, !.

xml_content(Dict, [Name], [Var]) :-
    atom(Name),
    memberchk(Name=Var, Dict),
    !.
xml_content(Dict, Content0, Content) :-
    maplist(xml_content_element(Dict), Content0, Content).

xml_content_element(Dict,
                    element(Tag, Attrs0, Content0),
                    element(Tag, Attrs, Content)) :-
    !,
    maplist(xml_attribute(Dict), Attrs0, Attrs),
    xml_content(Dict, Content0, Content).
xml_content_element(_, Element, Element).

xml_attribute(Dict, Attr=Name, Attr=Var) :-
    memberchk(Name=Var, Dict),
    !.
xml_attribute(_, Attr, Attr).