View source with raw comments or as raw
    1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker and Anjo Anjewierden
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2002-2020, University of Amsterdam
    7                              VU University Amsterdam
    8    All rights reserved.
    9
   10    Redistribution and use in source and binary forms, with or without
   11    modification, are permitted provided that the following conditions
   12    are met:
   13
   14    1. Redistributions of source code must retain the above copyright
   15       notice, this list of conditions and the following disclaimer.
   16
   17    2. Redistributions in binary form must reproduce the above copyright
   18       notice, this list of conditions and the following disclaimer in
   19       the documentation and/or other materials provided with the
   20       distribution.
   21
   22    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   24    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   25    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   26    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   27    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   28    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   29    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   30    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   31    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   32    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   33    POSSIBILITY OF SUCH DAMAGE.
   34*/
   35
   36:- module(html_write,
   37          [ reply_html_page/2,          % :Head, :Body
   38            reply_html_page/3,          % +Style, :Head, :Body
   39
   40                                        % Basic output routines
   41            page//1,                    % :Content
   42            page//2,                    % :Head, :Body
   43            page//3,                    % +Style, :Head, :Body
   44            html//1,                    % :Content
   45
   46                                        % Option processing
   47            html_set_options/1,         % +OptionList
   48            html_current_option/1,      % ?Option
   49
   50                                        % repositioning HTML elements
   51            html_post//2,               % +Id, :Content
   52            html_receive//1,            % +Id
   53            html_receive//2,            % +Id, :Handler
   54            xhtml_ns//2,                % +Id, +Value
   55            html_root_attribute//2,     % +Name, +Value
   56
   57            html/4,                     % {|html||quasi quotations|}
   58
   59                                        % Useful primitives for expanding
   60            html_begin//1,              % +EnvName[(Attribute...)]
   61            html_end//1,                % +EnvName
   62            html_quoted//1,             % +Text
   63            html_quoted_attribute//1,   % +Attribute
   64
   65                                        % Emitting the HTML code
   66            print_html/1,               % +List
   67            print_html/2,               % +Stream, +List
   68            html_print_length/2,        % +List, -Length
   69
   70                                        % Extension support
   71            (html_meta)/1,              % +Spec
   72            op(1150, fx, html_meta)
   73          ]).   74:- use_module(html_quasiquotations, [html/4]).   75:- autoload(library(apply),[maplist/3,maplist/4]).   76:- autoload(library(debug),[debug/3]).   77:- autoload(library(error),
   78	    [must_be/2,domain_error/2,instantiation_error/1]).   79:- autoload(library(lists),
   80	    [permutation/2,selectchk/3,append/3,select/4,list_to_set/2]).   81:- autoload(library(option),[option/2]).   82:- autoload(library(pairs),[group_pairs_by_key/2]).   83:- autoload(library(sgml),[xml_quote_cdata/3,xml_quote_attribute/3]).   84:- autoload(library(uri),[uri_encoded/3]).   85:- autoload(library(url),[www_form_encode/2]).   86:- autoload(library(http/http_dispatch), [http_location_by_id/2]).   87
   88% Quote output
   89:- set_prolog_flag(generate_debug_info, false).   90
   91:- meta_predicate
   92    reply_html_page(+, :, :),
   93    reply_html_page(:, :),
   94    html(:, -, +),
   95    page(:, -, +),
   96    page(:, :, -, +),
   97    pagehead(+, :, -, +),
   98    pagebody(+, :, -, +),
   99    html_receive(+, 3, -, +),
  100    html_post(+, :, -, +).  101
  102:- multifile
  103    expand//1,                      % +HTMLElement
  104    expand_attribute_value//1,      % +HTMLAttributeValue
  105    html_header_hook/1.             % +Style

Write HTML text

Most code doesn't need to use this directly; instead use library(http/http_server), which combines this library with the typical HTTP libraries that most servers need.

The purpose of this library is to simplify writing HTML pages. Of course, it is possible to use format/3 to write to the HTML stream directly, but this is generally not very satisfactory:

This module tries to remedy these problems. The idea is to translate a Prolog term into an HTML document. We use DCG for most of the generation.

International documents

The library supports the generation of international documents, but this is currently limited to using UTF-8 encoded HTML or XHTML documents. It is strongly recommended to use the following mime-type.

Content-type: text/html; charset=UTF-8

When generating XHTML documents, the output stream must be in UTF-8 encoding. */

  142                 /*******************************
  143                 *            SETTINGS          *
  144                 *******************************/
 html_set_options(+Options) is det
Set options for the HTML output. Options are stored in prolog flags to ensure proper multi-threaded behaviour where setting an option is local to the thread and new threads start with the options from the parent thread. Defined options are:
dialect(Dialect)
One of html4, xhtml or html5 (default). For compatibility reasons, html is accepted as an alias for html4.
doctype(+DocType)
Set the <|DOCTYPE DocType > line for page//1 and page//2.
content_type(+ContentType)
Set the Content-type for reply_html_page/3

Note that the doctype and content_type flags are covered by distinct prolog flags: html4_doctype, xhtml_doctype and html5_doctype and similar for the content type. The Dialect must be switched before doctype and content type.

  170html_set_options(Options) :-
  171    must_be(list, Options),
  172    set_options(Options).
  173
  174set_options([]).
  175set_options([H|T]) :-
  176    html_set_option(H),
  177    set_options(T).
  178
  179html_set_option(dialect(Dialect0)) :-
  180    !,
  181    must_be(oneof([html,html4,xhtml,html5]), Dialect0),
  182    (   html_version_alias(Dialect0, Dialect)
  183    ->  true
  184    ;   Dialect = Dialect0
  185    ),
  186    set_prolog_flag(html_dialect, Dialect).
  187html_set_option(doctype(Atom)) :-
  188    !,
  189    must_be(atom, Atom),
  190    current_prolog_flag(html_dialect, Dialect),
  191    dialect_doctype_flag(Dialect, Flag),
  192    set_prolog_flag(Flag, Atom).
  193html_set_option(content_type(Atom)) :-
  194    !,
  195    must_be(atom, Atom),
  196    current_prolog_flag(html_dialect, Dialect),
  197    dialect_content_type_flag(Dialect, Flag),
  198    set_prolog_flag(Flag, Atom).
  199html_set_option(O) :-
  200    domain_error(html_option, O).
  201
  202html_version_alias(html, html4).
 html_current_option(?Option) is nondet
True if Option is an active option for the HTML generator.
  208html_current_option(dialect(Dialect)) :-
  209    current_prolog_flag(html_dialect, Dialect).
  210html_current_option(doctype(DocType)) :-
  211    current_prolog_flag(html_dialect, Dialect),
  212    dialect_doctype_flag(Dialect, Flag),
  213    current_prolog_flag(Flag, DocType).
  214html_current_option(content_type(ContentType)) :-
  215    current_prolog_flag(html_dialect, Dialect),
  216    dialect_content_type_flag(Dialect, Flag),
  217    current_prolog_flag(Flag, ContentType).
  218
  219dialect_doctype_flag(html4, html4_doctype).
  220dialect_doctype_flag(html5, html5_doctype).
  221dialect_doctype_flag(xhtml, xhtml_doctype).
  222
  223dialect_content_type_flag(html4, html4_content_type).
  224dialect_content_type_flag(html5, html5_content_type).
  225dialect_content_type_flag(xhtml, xhtml_content_type).
  226
  227option_default(html_dialect, html5).
  228option_default(html4_doctype,
  229               'HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" \c
  230               "http://www.w3.org/TR/html4/loose.dtd"').
  231option_default(html5_doctype,
  232               'html').
  233option_default(xhtml_doctype,
  234               'html PUBLIC "-//W3C//DTD XHTML 1.0 \c
  235               Transitional//EN" \c
  236               "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"').
  237option_default(html4_content_type, 'text/html; charset=UTF-8').
  238option_default(html5_content_type, 'text/html; charset=UTF-8').
  239option_default(xhtml_content_type, 'application/xhtml+xml; charset=UTF-8').
 init_options is det
Initialise the HTML processing options.
  245init_options :-
  246    (   option_default(Name, Value),
  247        (   current_prolog_flag(Name, _)
  248        ->  true
  249        ;   create_prolog_flag(Name, Value, [])
  250        ),
  251        fail
  252    ;   true
  253    ).
  254
  255:- init_options.
 xml_header(-Header)
First line of XHTML document. Added by print_html/1.
  261xml_header('<?xml version=\'1.0\' encoding=\'UTF-8\'?>').
 ns(?Which, ?Atom)
Namespace declarations
  267ns(xhtml, 'http://www.w3.org/1999/xhtml').
  268
  269
  270                 /*******************************
  271                 *             PAGE             *
  272                 *******************************/
 page(+Content:dom)// is det
 page(+Head:dom, +Body:dom)// is det
Generate a page including the HTML <!DOCTYPE> header. The actual doctype is read from the option doctype as defined by html_set_options/1.
  281page(Content) -->
  282    doctype,
  283    html(html(Content)).
  284
  285page(Head, Body) -->
  286    page(default, Head, Body).
  287
  288page(Style, Head, Body) -->
  289    doctype,
  290    content_type,
  291    html_begin(html),
  292    pagehead(Style, Head),
  293    pagebody(Style, Body),
  294    html_end(html).
 doctype//
Emit the <DOCTYPE ... header. The doctype comes from the option doctype(DOCTYPE) (see html_set_options/1). Setting the doctype to '' (empty atom) suppresses the header completely. This is to avoid a IE bug in processing AJAX output ...
  303doctype -->
  304    { html_current_option(doctype(DocType)),
  305      DocType \== ''
  306    },
  307    !,
  308    [ '<!DOCTYPE ', DocType, '>' ].
  309doctype -->
  310    [].
  311
  312content_type -->
  313    { html_current_option(content_type(Type))
  314    },
  315    !,
  316    html_post(head, meta([ 'http-equiv'('content-type'),
  317                           content(Type)
  318                         ], [])).
  319content_type -->
  320    { html_current_option(dialect(html5)) },
  321    !,
  322    html_post(head, meta('charset=UTF-8')).
  323content_type -->
  324    [].
  325
  326pagehead(_, Head) -->
  327    { functor(Head, head, _)
  328    },
  329    !,
  330    html(Head).
  331pagehead(Style, Head) -->
  332    { strip_module(Head, M, _),
  333      hook_module(M, HM, head//2)
  334    },
  335    HM:head(Style, Head),
  336    !.
  337pagehead(_, Head) -->
  338    { strip_module(Head, M, _),
  339      hook_module(M, HM, head//1)
  340    },
  341    HM:head(Head),
  342    !.
  343pagehead(_, Head) -->
  344    html(head(Head)).
  345
  346
  347pagebody(_, Body) -->
  348    { functor(Body, body, _)
  349    },
  350    !,
  351    html(Body).
  352pagebody(Style, Body) -->
  353    { strip_module(Body, M, _),
  354      hook_module(M, HM, body//2)
  355    },
  356    HM:body(Style, Body),
  357    !.
  358pagebody(_, Body) -->
  359    { strip_module(Body, M, _),
  360      hook_module(M, HM, body//1)
  361    },
  362    HM:body(Body),
  363    !.
  364pagebody(_, Body) -->
  365    html(body(Body)).
  366
  367
  368hook_module(M, M, PI) :-
  369    current_predicate(M:PI),
  370    !.
  371hook_module(_, user, PI) :-
  372    current_predicate(user:PI).
 html(+Content:dom)// is det
Generate HTML from Content. Generates a token sequence for print_html/2.
  379html(Spec) -->
  380    { strip_module(Spec, M, T) },
  381    qhtml(T, M).
  382
  383qhtml(Var, _) -->
  384    { var(Var),
  385      !,
  386      instantiation_error(Var)
  387    }.
  388qhtml([], _) -->
  389    !,
  390    [].
  391qhtml([H|T], M) -->
  392    !,
  393    html_expand(H, M),
  394    qhtml(T, M).
  395qhtml(X, M) -->
  396    html_expand(X, M).
  397
  398html_expand(Var, _) -->
  399    { var(Var),
  400      !,
  401      instantiation_error(Var)
  402    }.
  403html_expand(Term, Module) -->
  404    do_expand(Term, Module),
  405    !.
  406html_expand(Term, _Module) -->
  407    { print_message(error, html(expand_failed(Term))) }.
  408
  409
  410do_expand(Token, _) -->                 % call user hooks
  411    expand(Token),
  412    !.
  413do_expand(Fmt-Args, _) -->
  414    !,
  415    { format(string(String), Fmt, Args)
  416    },
  417    html_quoted(String).
  418do_expand(\List, Module) -->
  419    { is_list(List)
  420    },
  421    !,
  422    raw(List, Module).
  423do_expand(\Term, Module, In, Rest) :-
  424    !,
  425    call(Module:Term, In, Rest).
  426do_expand(Module:Term, _) -->
  427    !,
  428    qhtml(Term, Module).
  429do_expand(&(Entity), _) -->
  430    !,
  431    {   integer(Entity)
  432    ->  format(string(String), '&#~d;', [Entity])
  433    ;   format(string(String), '&~w;', [Entity])
  434    },
  435    [ String ].
  436do_expand(Token, _) -->
  437    { atomic(Token)
  438    },
  439    !,
  440    html_quoted(Token).
  441do_expand(element(Env, Attributes, Contents), M) -->
  442    !,
  443    (   { Contents == [],
  444          html_current_option(dialect(xhtml))
  445        }
  446    ->  xhtml_empty(Env, Attributes)
  447    ;   html_begin(Env, Attributes),
  448        qhtml(Env, Contents, M),
  449        html_end(Env)
  450    ).
  451do_expand(Term, M) -->
  452    { Term =.. [Env, Contents]
  453    },
  454    !,
  455    (   { layout(Env, _, empty)
  456        }
  457    ->  html_begin(Env, Contents)
  458    ;   (   { Contents == [],
  459              html_current_option(dialect(xhtml))
  460            }
  461        ->  xhtml_empty(Env, [])
  462        ;   html_begin(Env),
  463            qhtml(Env, Contents, M),
  464            html_end(Env)
  465        )
  466    ).
  467do_expand(Term, M) -->
  468    { Term =.. [Env, Attributes, Contents],
  469      check_non_empty(Contents, Env, Term)
  470    },
  471    !,
  472    (   { Contents == [],
  473          html_current_option(dialect(xhtml))
  474        }
  475    ->  xhtml_empty(Env, Attributes)
  476    ;   html_begin(Env, Attributes),
  477        qhtml(Env, Contents, M),
  478        html_end(Env)
  479    ).
  480
  481qhtml(Env, Contents, M) -->
  482    { cdata_element(Env),
  483      phrase(cdata(Contents, M), Tokens)
  484    },
  485    !,
  486    [ cdata(Env, Tokens) ].
  487qhtml(_, Contents, M) -->
  488    qhtml(Contents, M).
  489
  490
  491check_non_empty([], _, _) :- !.
  492check_non_empty(_, Tag, Term) :-
  493    layout(Tag, _, empty),
  494    !,
  495    print_message(warning,
  496                  format('Using empty element with content: ~p', [Term])).
  497check_non_empty(_, _, _).
  498
  499cdata(List, M) -->
  500    { is_list(List) },
  501    !,
  502    raw(List, M).
  503cdata(One, M) -->
  504    raw_element(One, M).
 raw(+List, +Module)// is det
Emit unquoted (raw) output used for scripts, etc.
  510raw([], _) -->
  511    [].
  512raw([H|T], Module) -->
  513    raw_element(H, Module),
  514    raw(T, Module).
  515
  516raw_element(Var, _) -->
  517    { var(Var),
  518      !,
  519      instantiation_error(Var)
  520    }.
  521raw_element(\List, Module) -->
  522    { is_list(List)
  523    },
  524    !,
  525    raw(List, Module).
  526raw_element(\Term, Module, In, Rest) :-
  527    !,
  528    call(Module:Term, In, Rest).
  529raw_element(Module:Term, _) -->
  530    !,
  531    raw_element(Term, Module).
  532raw_element(Fmt-Args, _) -->
  533    !,
  534    { format(string(S), Fmt, Args) },
  535    [S].
  536raw_element(Value, _) -->
  537    { must_be(atomic, Value) },
  538    [Value].
 html_begin(+Env)// is det
 html_end(+End)// is det
For html_begin//1, Env is a term Env(Attributes); for html_end//1 it is the plain environment name. Used for exceptional cases. Normal applications use html//1. The following two fragments are identical, where we prefer the first as it is more concise and less error-prone.
        html(table(border=1, \table_content))
        html_begin(table(border=1)
        table_content,
        html_end(table)
  559html_begin(Env) -->
  560    { Env =.. [Name|Attributes]
  561    },
  562    html_begin(Name, Attributes).
  563
  564html_begin(Env, Attributes) -->
  565    pre_open(Env),
  566    [<],
  567    [Env],
  568    attributes(Env, Attributes),
  569    (   { layout(Env, _, empty),
  570          html_current_option(dialect(xhtml))
  571        }
  572    ->  ['/>']
  573    ;   [>]
  574    ),
  575    post_open(Env).
  576
  577html_end(Env)   -->                     % empty element or omited close
  578    { layout(Env, _, -),
  579      html_current_option(dialect(html))
  580    ; layout(Env, _, empty)
  581    },
  582    !,
  583    [].
  584html_end(Env)   -->
  585    pre_close(Env),
  586    ['</'],
  587    [Env],
  588    ['>'],
  589    post_close(Env).
 xhtml_empty(+Env, +Attributes)// is det
Emit element in xhtml mode with empty content.
  595xhtml_empty(Env, Attributes) -->
  596    pre_open(Env),
  597    [<],
  598    [Env],
  599    attributes(Attributes),
  600    ['/>'].
 xhtml_ns(+Id, +Value)//
Demand an xmlns:id=Value in the outer html tag. This uses the html_post/2 mechanism to post to the xmlns channel. Rdfa (http://www.w3.org/2006/07/SWD/RDFa/syntax/), embedding RDF in (x)html provides a typical usage scenario where we want to publish the required namespaces in the header. We can define:
rdf_ns(Id) -->
        { rdf_global_id(Id:'', Value) },
        xhtml_ns(Id, Value).

After which we can use rdf_ns//1 as a normal rule in html//1 to publish namespaces from library(semweb/rdf_db). Note that this macro only has effect if the dialect is set to xhtml. In html mode it is silently ignored.

The required xmlns receiver is installed by html_begin//1 using the html tag and thus is present in any document that opens the outer html environment through this library.

  625xhtml_ns(Id, Value) -->
  626    { html_current_option(dialect(xhtml)) },
  627    !,
  628    html_post(xmlns, \attribute(xmlns:Id=Value)).
  629xhtml_ns(_, _) -->
  630    [].
 html_root_attribute(+Name, +Value)//
Add an attribute to the HTML root element of the page. For example:
    html(div(...)),
    html_root_attribute(lang, en),
    ...
  643html_root_attribute(Name, Value) -->
  644    html_post(html_begin, \attribute(Name=Value)).
 attributes(+Env, +Attributes)// is det
Emit attributes for Env. Adds XHTML namespace declaration to the html tag if not provided by the caller.
  651attributes(html, L) -->
  652    !,
  653    (   { html_current_option(dialect(xhtml)) }
  654    ->  (   { option(xmlns(_), L) }
  655        ->  attributes(L)
  656        ;   { ns(xhtml, NS) },
  657            attributes([xmlns(NS)|L])
  658        ),
  659        html_receive(xmlns)
  660    ;   attributes(L),
  661        html_noreceive(xmlns)
  662    ),
  663    html_receive(html_begin).
  664attributes(_, L) -->
  665    attributes(L).
  666
  667attributes([]) -->
  668    !,
  669    [].
  670attributes([H|T]) -->
  671    !,
  672    attribute(H),
  673    attributes(T).
  674attributes(One) -->
  675    attribute(One).
  676
  677attribute(Name=Value) -->
  678    !,
  679    [' '], name(Name), [ '="' ],
  680    attribute_value(Value),
  681    ['"'].
  682attribute(NS:Term) -->
  683    !,
  684    { Term =.. [Name, Value]
  685    },
  686    !,
  687    attribute((NS:Name)=Value).
  688attribute(Term) -->
  689    { Term =.. [Name, Value]
  690    },
  691    !,
  692    attribute(Name=Value).
  693attribute(Atom) -->                     % Value-abbreviated attribute
  694    { atom(Atom)
  695    },
  696    [ ' ', Atom ].
  697
  698name(NS:Name) -->
  699    !,
  700    [NS, :, Name].
  701name(Name) -->
  702    [ Name ].
 attribute_value(+Value) is det
Print an attribute value. Value is either atomic or one of the following terms:

The hook expand_attribute_value//1 can be defined to provide additional `function like' translations. For example, http_dispatch.pl defines location_by_id(ID) to refer to a location on the current server based on the handler id. See http_location_by_id/2.

  724attribute_value(List) -->
  725    { is_list(List) },
  726    !,
  727    attribute_value_m(List).
  728attribute_value(Value) -->
  729    attribute_value_s(Value).
  730
  731% emit a single attribute value
  732
  733attribute_value_s(Var) -->
  734    { var(Var),
  735      !,
  736      instantiation_error(Var)
  737    }.
  738attribute_value_s(A+B) -->
  739    !,
  740    attribute_value(A),
  741    (   { is_list(B) }
  742    ->  (   { B == [] }
  743        ->  []
  744        ;   [?], search_parameters(B)
  745        )
  746    ;   attribute_value(B)
  747    ).
  748attribute_value_s(encode(Value)) -->
  749    !,
  750    { uri_encoded(query_value, Value, Encoded) },
  751    [ Encoded ].
  752attribute_value_s(Value) -->
  753    expand_attribute_value(Value),
  754    !.
  755attribute_value_s(Fmt-Args) -->
  756    !,
  757    { format(string(Value), Fmt, Args) },
  758    html_quoted_attribute(Value).
  759attribute_value_s(Value) -->
  760    html_quoted_attribute(Value).
  761
  762search_parameters([H|T]) -->
  763    search_parameter(H),
  764    (   {T == []}
  765    ->  []
  766    ;   ['&amp;'],
  767        search_parameters(T)
  768    ).
  769
  770search_parameter(Var) -->
  771    { var(Var),
  772      !,
  773      instantiation_error(Var)
  774    }.
  775search_parameter(Name=Value) -->
  776    { www_form_encode(Value, Encoded) },
  777    [Name, =, Encoded].
  778search_parameter(Term) -->
  779    { Term =.. [Name, Value],
  780      !,
  781      www_form_encode(Value, Encoded)
  782    },
  783    [Name, =, Encoded].
  784search_parameter(Term) -->
  785    { domain_error(search_parameter, Term)
  786    }.
 attribute_value_m(+List)//
Used for multi-valued attributes, such as class-lists. E.g.,
      body(class([c1, c2]), Body)

Emits <body class="c1 c2"> ...

  798attribute_value_m([]) -->
  799    [].
  800attribute_value_m([H|T]) -->
  801    attribute_value_s(H),
  802    (   { T == [] }
  803    ->  []
  804    ;   [' '],
  805        attribute_value_m(T)
  806    ).
  807
  808
  809                 /*******************************
  810                 *         QUOTING RULES        *
  811                 *******************************/
 html_quoted(Text)// is det
Quote the value for normal (CDATA) text. Note that text appearing in the document structure is normally quoted using these rules. I.e. the following emits properly quoted bold text regardless of the content of Text:
        html(b(Text))
To be done
- Assumes UTF-8 encoding of the output.
  826html_quoted(Text) -->
  827    { xml_quote_cdata(Text, Quoted, utf8) },
  828    [ Quoted ].
 html_quoted_attribute(+Text)// is det
Quote the value according to the rules for tag-attributes included in double-quotes. Note that -like html_quoted//1-, attributed values printed through html//1 are quoted atomatically.
To be done
- Assumes UTF-8 encoding of the output.
  839html_quoted_attribute(Text) -->
  840    { xml_quote_attribute(Text, Quoted, utf8) },
  841    [ Quoted ].
 cdata_element(?Element)
True when Element contains declared CDATA and thus only </ needs to be escaped.
  848cdata_element(script).
  849cdata_element(style).
  850
  851
  852                 /*******************************
  853                 *      REPOSITIONING HTML      *
  854                 *******************************/
 html_post(+Id, :HTML)// is det
Reposition HTML to the receiving Id. The html_post//2 call processes HTML using html//1. Embedded \-commands are executed by mailman/1 from print_html/1 or html_print_length/2. These commands are called in the calling context of the html_post//2 call.

A typical usage scenario is to get required CSS links in the document head in a reusable fashion. First, we define css//1 as:

css(URL) -->
        html_post(css,
                  link([ type('text/css'),
                         rel('stylesheet'),
                         href(URL)
                       ])).

Next we insert the unique CSS links, in the pagehead using the following call to reply_html_page/2:

        reply_html_page([ title(...),
                          \html_receive(css)
                        ],
                        ...)
  886html_post(Id, Content) -->
  887    { strip_module(Content, M, C) },
  888    [ mailbox(Id, post(M, C)) ].
 html_receive(+Id)// is det
Receive posted HTML tokens. Unique sequences of tokens posted with html_post//2 are inserted at the location where html_receive//1 appears.
See also
- The local predicate sorted_html//1 handles the output of html_receive//1.
- html_receive//2 allows for post-processing the posted material.
  901html_receive(Id) -->
  902    html_receive(Id, sorted_html).
 html_receive(+Id, :Handler)// is det
This extended version of html_receive//1 causes Handler to be called to process all messages posted to the channal at the time output is generated. Handler is called as below, where PostedTerms is a list of Module:Term created from calls to html_post//2. Module is the context module of html_post and Term is the unmodified term. Members in PostedTerms are in the order posted and may contain duplicates.
  phrase(Handler, PostedTerms, HtmlTerms, Rest)

Typically, Handler collects the posted terms, creating a term suitable for html//1 and finally calls html//1.

  921html_receive(Id, Handler) -->
  922    { strip_module(Handler, M, P) },
  923    [ mailbox(Id, accept(M:P, _)) ].
 html_noreceive(+Id)// is det
As html_receive//1, but discard posted messages.
  929html_noreceive(Id) -->
  930    [ mailbox(Id, ignore(_,_)) ].
 mailman(+Tokens) is det
Collect posted tokens and copy them into the receiving mailboxes. Mailboxes may produce output for each other, but not cyclic. The current scheme to resolve this is rather naive: It simply permutates the mailbox resolution order until it found a working one. Before that, it puts head and script boxes at the end.
  941mailman(Tokens) :-
  942    (   html_token(mailbox(_, accept(_, Accepted)), Tokens)
  943    ->  true
  944    ),
  945    var(Accepted),                 % not yet executed
  946    !,
  947    mailboxes(Tokens, Boxes),
  948    keysort(Boxes, Keyed),
  949    group_pairs_by_key(Keyed, PerKey),
  950    move_last(PerKey, script, PerKey1),
  951    move_last(PerKey1, head, PerKey2),
  952    (   permutation(PerKey2, PerKeyPerm),
  953        (   mail_ids(PerKeyPerm)
  954        ->  !
  955        ;   debug(html(mailman),
  956                  'Failed mail delivery order; retrying', []),
  957            fail
  958        )
  959    ->  true
  960    ;   print_message(error, html(cyclic_mailboxes))
  961    ).
  962mailman(_).
  963
  964move_last(Box0, Id, Box) :-
  965    selectchk(Id-List, Box0, Box1),
  966    !,
  967    append(Box1, [Id-List], Box).
  968move_last(Box, _, Box).
 html_token(?Token, +Tokens) is nondet
True if Token is a token in the token set. This is like member, but the toplevel list may contain cdata(Elem, Tokens).
  975html_token(Token, [H|T]) :-
  976    html_token_(T, H, Token).
  977
  978html_token_(_, Token, Token) :- !.
  979html_token_(_, cdata(_,Tokens), Token) :-
  980    html_token(Token, Tokens).
  981html_token_([H|T], _, Token) :-
  982    html_token_(T, H, Token).
 mailboxes(+Tokens, -MailBoxes) is det
Get all mailboxes from the token set.
  988mailboxes(Tokens, MailBoxes) :-
  989    mailboxes(Tokens, MailBoxes, []).
  990
  991mailboxes([], List, List).
  992mailboxes([mailbox(Id, Value)|T0], [Id-Value|T], Tail) :-
  993    !,
  994    mailboxes(T0, T, Tail).
  995mailboxes([cdata(_Type, Tokens)|T0], Boxes, Tail) :-
  996    !,
  997    mailboxes(Tokens, Boxes, Tail0),
  998    mailboxes(T0, Tail0, Tail).
  999mailboxes([_|T0], T, Tail) :-
 1000    mailboxes(T0, T, Tail).
 1001
 1002mail_ids([]).
 1003mail_ids([H|T0]) :-
 1004    mail_id(H, NewPosts),
 1005    add_new_posts(NewPosts, T0, T),
 1006    mail_ids(T).
 1007
 1008mail_id(Id-List, NewPosts) :-
 1009    mail_handlers(List, Boxes, Content),
 1010    (   Boxes = [accept(MH:Handler, In)]
 1011    ->  extend_args(Handler, Content, Goal),
 1012        phrase(MH:Goal, In),
 1013        mailboxes(In, NewBoxes),
 1014        keysort(NewBoxes, Keyed),
 1015        group_pairs_by_key(Keyed, NewPosts)
 1016    ;   Boxes = [ignore(_, _)|_]
 1017    ->  NewPosts = []
 1018    ;   Boxes = [accept(_,_),accept(_,_)|_]
 1019    ->  print_message(error, html(multiple_receivers(Id))),
 1020        NewPosts = []
 1021    ;   print_message(error, html(no_receiver(Id))),
 1022        NewPosts = []
 1023    ).
 1024
 1025add_new_posts([], T, T).
 1026add_new_posts([Id-Posts|NewT], T0, T) :-
 1027    (   select(Id-List0, T0, Id-List, T1)
 1028    ->  append(List0, Posts, List)
 1029    ;   debug(html(mailman), 'Stuck with new posts on ~q', [Id]),
 1030        fail
 1031    ),
 1032    add_new_posts(NewT, T1, T).
 mail_handlers(+Boxes, -Handlers, -Posters) is det
Collect all post(Module,HTML) into Posters and the remainder in Handlers. Handlers consists of accept(Handler, Tokens) and ignore(_,_).
 1041mail_handlers([], [], []).
 1042mail_handlers([post(Module,HTML)|T0], H, [Module:HTML|T]) :-
 1043    !,
 1044    mail_handlers(T0, H, T).
 1045mail_handlers([H|T0], [H|T], C) :-
 1046    mail_handlers(T0, T, C).
 1047
 1048extend_args(Term, Extra, NewTerm) :-
 1049    Term =.. [Name|Args],
 1050    append(Args, [Extra], NewArgs),
 1051    NewTerm =.. [Name|NewArgs].
 sorted_html(+Content:list)// is det
Default handlers for html_receive//1. It sorts the posted objects to create a unique list.
bug
- Elements can differ just on the module. Ideally we should phrase all members, sort the list of list of tokens and emit the result. Can we do better?
 1062sorted_html(List) -->
 1063    { sort(List, Unique) },
 1064    html(Unique).
 head_html(+Content:list)// is det
Handler for html_receive(head). Unlike sorted_html//1, it calls a user hook html_head_expansion/2 to process the collected head material into a term suitable for html//1.
To be done
- This has been added to facilitate html_head.pl, an experimental library for dealing with css and javascript resources. It feels a bit like a hack, but for now I do not know a better solution.
 1077head_html(List) -->
 1078    { list_to_set(List, Unique),
 1079      html_expand_head(Unique, NewList)
 1080    },
 1081    html(NewList).
 1082
 1083:- multifile
 1084    html_head_expansion/2. 1085
 1086html_expand_head(List0, List) :-
 1087    html_head_expansion(List0, List1),
 1088    List0 \== List1,
 1089    !,
 1090    html_expand_head(List1, List).
 1091html_expand_head(List, List).
 1092
 1093
 1094                 /*******************************
 1095                 *             LAYOUT           *
 1096                 *******************************/
 1097
 1098pre_open(Env) -->
 1099    { layout(Env, N-_, _)
 1100    },
 1101    !,
 1102    [ nl(N) ].
 1103pre_open(_) --> [].
 1104
 1105post_open(Env) -->
 1106    { layout(Env, _-N, _)
 1107    },
 1108    !,
 1109    [ nl(N) ].
 1110post_open(_) -->
 1111    [].
 1112
 1113pre_close(head) -->
 1114    !,
 1115    html_receive(head, head_html),
 1116    { layout(head, _, N-_) },
 1117    [ nl(N) ].
 1118pre_close(Env) -->
 1119    { layout(Env, _, N-_)
 1120    },
 1121    !,
 1122    [ nl(N) ].
 1123pre_close(_) -->
 1124    [].
 1125
 1126post_close(Env) -->
 1127    { layout(Env, _, _-N)
 1128    },
 1129    !,
 1130    [ nl(N) ].
 1131post_close(_) -->
 1132    [].
 layout(+Tag, -Open, -Close) is det
Define required newlines before and after tags. This table is rather incomplete. New rules can be added to this multifile predicate.
Arguments:
Tag- Name of the tag
Open- Tuple M-N, where M is the number of lines before the tag and N after.
Close- Either as Open, or the atom - (minus) to omit the close-tag or empty to indicate the element has no content model.
To be done
- Complete table
 1149:- multifile
 1150    layout/3. 1151
 1152layout(table,      2-1, 1-2).
 1153layout(blockquote, 2-1, 1-2).
 1154layout(pre,        2-1, 0-2).
 1155layout(textarea,   1-1, 0-1).
 1156layout(center,     2-1, 1-2).
 1157layout(dl,         2-1, 1-2).
 1158layout(ul,         1-1, 1-1).
 1159layout(ol,         2-1, 1-2).
 1160layout(form,       2-1, 1-2).
 1161layout(frameset,   2-1, 1-2).
 1162layout(address,    2-1, 1-2).
 1163
 1164layout(head,       1-1, 1-1).
 1165layout(body,       1-1, 1-1).
 1166layout(script,     1-1, 1-1).
 1167layout(style,      1-1, 1-1).
 1168layout(select,     1-1, 1-1).
 1169layout(map,        1-1, 1-1).
 1170layout(html,       1-1, 1-1).
 1171layout(caption,    1-1, 1-1).
 1172layout(applet,     1-1, 1-1).
 1173
 1174layout(tr,         1-0, 0-1).
 1175layout(option,     1-0, 0-1).
 1176layout(li,         1-0, 0-1).
 1177layout(dt,         1-0, -).
 1178layout(dd,         0-0, -).
 1179layout(title,      1-0, 0-1).
 1180
 1181layout(h1,         2-0, 0-2).
 1182layout(h2,         2-0, 0-2).
 1183layout(h3,         2-0, 0-2).
 1184layout(h4,         2-0, 0-2).
 1185
 1186layout(iframe,     1-1, 1-1).
 1187
 1188layout(hr,         1-1, empty).         % empty elements
 1189layout(br,         0-1, empty).
 1190layout(img,        0-0, empty).
 1191layout(meta,       1-1, empty).
 1192layout(base,       1-1, empty).
 1193layout(link,       1-1, empty).
 1194layout(input,      0-0, empty).
 1195layout(frame,      1-1, empty).
 1196layout(col,        0-0, empty).
 1197layout(area,       1-0, empty).
 1198layout(input,      1-0, empty).
 1199layout(param,      1-0, empty).
 1200
 1201layout(p,          2-1, -).             % omited close
 1202layout(td,         0-0, 0-0).
 1203
 1204layout(div,        1-0, 0-1).
 1205
 1206                 /*******************************
 1207                 *           PRINTING           *
 1208                 *******************************/
 print_html(+List) is det
 print_html(+Out:stream, +List) is det
Print list of atoms and layout instructions. Currently used layout instructions:
nl(N)
Use at minimum N newlines here.
mailbox(Id, Box)
Repositioned tokens (see html_post//2 and html_receive//2)
 1223print_html(List) :-
 1224    current_output(Out),
 1225    mailman(List),
 1226    write_html(List, Out).
 1227print_html(Out, List) :-
 1228    (   html_current_option(dialect(xhtml))
 1229    ->  stream_property(Out, encoding(Enc)),
 1230        (   Enc == utf8
 1231        ->  true
 1232        ;   print_message(warning, html(wrong_encoding(Out, Enc)))
 1233        ),
 1234        xml_header(Hdr),
 1235        write(Out, Hdr), nl(Out)
 1236    ;   true
 1237    ),
 1238    mailman(List),
 1239    write_html(List, Out),
 1240    flush_output(Out).
 1241
 1242write_html([], _).
 1243write_html([nl(N)|T], Out) :-
 1244    !,
 1245    join_nl(T, N, Lines, T2),
 1246    write_nl(Lines, Out),
 1247    write_html(T2, Out).
 1248write_html([mailbox(_, Box)|T], Out) :-
 1249    !,
 1250    (   Box = accept(_, Accepted)
 1251    ->  write_html(Accepted, Out)
 1252    ;   true
 1253    ),
 1254    write_html(T, Out).
 1255write_html([cdata(Env, Tokens)|T], Out) :-
 1256    !,
 1257    with_output_to(string(CDATA), write_html(Tokens, current_output)),
 1258    valid_cdata(Env, CDATA),
 1259    write(Out, CDATA),
 1260    write_html(T, Out).
 1261write_html([H|T], Out) :-
 1262    write(Out, H),
 1263    write_html(T, Out).
 1264
 1265join_nl([nl(N0)|T0], N1, N, T) :-
 1266    !,
 1267    N2 is max(N0, N1),
 1268    join_nl(T0, N2, N, T).
 1269join_nl(L, N, N, L).
 1270
 1271write_nl(0, _) :- !.
 1272write_nl(N, Out) :-
 1273    nl(Out),
 1274    N1 is N - 1,
 1275    write_nl(N1, Out).
 valid_cdata(+Env, +String) is det
True when String is valid content for a CDATA element such as <script>. This implies it cannot contain </script/. There is no escape for this and the script generator must use a work-around using features of the script language. For example, when using JavaScript, "</script>" can be written as "<\/script>".
Errors
- domain_error(cdata, String)
See also
- write_json/2, js_arg//1.
 1289valid_cdata(Env, String) :-
 1290    atomics_to_string(['</', Env, '>'], End),
 1291    sub_atom_icasechk(String, _, End),
 1292    !,
 1293    domain_error(cdata, String).
 1294valid_cdata(_, _).
 html_print_length(+List, -Len) is det
Determine the content length of a token list produced using html//1. Here is an example on how this is used to output an HTML compatible to HTTP:
        phrase(html(DOM), Tokens),
        html_print_length(Tokens, Len),
        format('Content-type: text/html; charset=UTF-8~n'),
        format('Content-length: ~d~n~n', [Len]),
        print_html(Tokens)
 1310html_print_length(List, Len) :-
 1311    mailman(List),
 1312    (   html_current_option(dialect(xhtml))
 1313    ->  xml_header(Hdr),
 1314        atom_length(Hdr, L0),
 1315        L1 is L0+1                  % one for newline
 1316    ;   L1 = 0
 1317    ),
 1318    html_print_length(List, L1, Len).
 1319
 1320html_print_length([], L, L).
 1321html_print_length([nl(N)|T], L0, L) :-
 1322    !,
 1323    join_nl(T, N, Lines, T1),
 1324    L1 is L0 + Lines,               % assume only \n!
 1325    html_print_length(T1, L1, L).
 1326html_print_length([mailbox(_, Box)|T], L0, L) :-
 1327    !,
 1328    (   Box = accept(_, Accepted)
 1329    ->  html_print_length(Accepted, L0, L1)
 1330    ;   L1 = L0
 1331    ),
 1332    html_print_length(T, L1, L).
 1333html_print_length([cdata(_, CDATA)|T], L0, L) :-
 1334    !,
 1335    html_print_length(CDATA, L0, L1),
 1336    html_print_length(T, L1, L).
 1337html_print_length([H|T], L0, L) :-
 1338    atom_length(H, Hlen),
 1339    L1 is L0+Hlen,
 1340    html_print_length(T, L1, L).
 reply_html_page(:Head, :Body) is det
 reply_html_page(+Style, :Head, :Body) is det
Provide the complete reply as required by http_wrapper.pl for a page constructed from Head and Body. The HTTP Content-type is provided by html_current_option/1.
 1350reply_html_page(Head, Body) :-
 1351    reply_html_page(default, Head, Body).
 1352reply_html_page(Style, Head, Body) :-
 1353    html_current_option(content_type(Type)),
 1354    phrase(page(Style, Head, Body), HTML),
 1355    forall(html_header_hook(Style), true),
 1356    format('Content-type: ~w~n~n', [Type]),
 1357    print_html(HTML).
 html_header_hook(+Style) is nondet
This multifile hook is called just before the Content-type header is emitted. It allows for emitting additional headers depending on the first argument of reply_html_page/3.
 1368                 /*******************************
 1369                 *     META-PREDICATE SUPPORT   *
 1370                 *******************************/
 html_meta(+Heads) is det
This directive can be used to declare that an HTML rendering rule takes HTML content as argument. It has two effects. It emits the appropriate meta_predicate/1 and instructs the built-in editor (PceEmacs) to provide proper colouring for the arguments. The arguments in Head are the same as for meta_predicate or can be constant html. For example:
:- html_meta
      page(html,html,?,?).
 1386html_meta(Spec) :-
 1387    throw(error(context_error(nodirective, html_meta(Spec)), _)).
 1388
 1389html_meta_decls(Var, _, _) :-
 1390    var(Var),
 1391    !,
 1392    instantiation_error(Var).
 1393html_meta_decls((A,B), (MA,MB), [MH|T]) :-
 1394    !,
 1395    html_meta_decl(A, MA, MH),
 1396    html_meta_decls(B, MB, T).
 1397html_meta_decls(A, MA, [MH]) :-
 1398    html_meta_decl(A, MA, MH).
 1399
 1400html_meta_decl(Head, MetaHead,
 1401               html_write:html_meta_head(GenHead, Module, Head)) :-
 1402    functor(Head, Name, Arity),
 1403    functor(GenHead, Name, Arity),
 1404    prolog_load_context(module, Module),
 1405    Head =.. [Name|HArgs],
 1406    maplist(html_meta_decl, HArgs, MArgs),
 1407    MetaHead =.. [Name|MArgs].
 1408
 1409html_meta_decl(html, :) :- !.
 1410html_meta_decl(Meta, Meta).
 1411
 1412system:term_expansion((:- html_meta(Heads)),
 1413                      [ (:- meta_predicate(Meta))
 1414                      | MetaHeads
 1415                      ]) :-
 1416    html_meta_decls(Heads, Meta, MetaHeads).
 1417
 1418:- multifile
 1419    html_meta_head/3. 1420
 1421html_meta_colours(Head, Goal, built_in-Colours) :-
 1422    Head =.. [_|MArgs],
 1423    Goal =.. [_|Args],
 1424    maplist(meta_colours, MArgs, Args, Colours).
 1425
 1426meta_colours(html, HTML, Colours) :-
 1427    !,
 1428    html_colours(HTML, Colours).
 1429meta_colours(I, _, Colours) :-
 1430    integer(I), I>=0,
 1431    !,
 1432    Colours = meta(I).
 1433meta_colours(_, _, classify).
 1434
 1435html_meta_called(Head, Goal, Called) :-
 1436    Head =.. [_|MArgs],
 1437    Goal =.. [_|Args],
 1438    meta_called(MArgs, Args, Called, []).
 1439
 1440meta_called([], [], Called, Called).
 1441meta_called([html|MT], [A|AT], Called, Tail) :-
 1442    !,
 1443    phrase(called_by(A), Called, Tail1),
 1444    meta_called(MT, AT, Tail1, Tail).
 1445meta_called([0|MT], [A|AT], [A|CT0], CT) :-
 1446    !,
 1447    meta_called(MT, AT, CT0, CT).
 1448meta_called([I|MT], [A|AT], [A+I|CT0], CT) :-
 1449    integer(I), I>0,
 1450    !,
 1451    meta_called(MT, AT, CT0, CT).
 1452meta_called([_|MT], [_|AT], Called, Tail) :-
 1453    !,
 1454    meta_called(MT, AT, Called, Tail).
 1455
 1456
 1457:- html_meta
 1458    html(html,?,?),
 1459    page(html,?,?),
 1460    page(html,html,?,?),
 1461    page(+,html,html,?,?),
 1462    pagehead(+,html,?,?),
 1463    pagebody(+,html,?,?),
 1464    reply_html_page(html,html),
 1465    reply_html_page(+,html,html),
 1466    html_post(+,html,?,?). 1467
 1468
 1469                 /*******************************
 1470                 *      PCE EMACS SUPPORT       *
 1471                 *******************************/
 1472
 1473:- multifile
 1474    prolog_colour:goal_colours/2,
 1475    prolog_colour:style/2,
 1476    prolog_colour:message//1,
 1477    prolog:called_by/2. 1478
 1479prolog_colour:goal_colours(Goal, Colours) :-
 1480    html_meta_head(Goal, _Module, Head),
 1481    html_meta_colours(Head, Goal, Colours).
 1482prolog_colour:goal_colours(html_meta(_),
 1483                           built_in-[meta_declarations([html])]).
 1484
 1485                                        % TBD: Check with do_expand!
 1486html_colours(Var, classify) :-
 1487    var(Var),
 1488    !.
 1489html_colours(\List, html_raw-[list-Colours]) :-
 1490    is_list(List),
 1491    !,
 1492    list_colours(List, Colours).
 1493html_colours(\_, html_call-[dcg]) :- !.
 1494html_colours(_:Term, built_in-[classify,Colours]) :-
 1495    !,
 1496    html_colours(Term, Colours).
 1497html_colours(&(Entity), functor-[entity(Entity)]) :- !.
 1498html_colours(List, list-ListColours) :-
 1499    List = [_|_],
 1500    !,
 1501    list_colours(List, ListColours).
 1502html_colours(Format-Args, functor-[FormatColor,ArgsColors]) :-
 1503    !,
 1504    format_colours(Format, FormatColor),
 1505    format_arg_colours(Args, Format, ArgsColors).
 1506html_colours(Term, TermColours) :-
 1507    compound(Term),
 1508    compound_name_arguments(Term, Name, Args),
 1509    Name \== '.',
 1510    !,
 1511    (   Args = [One]
 1512    ->  TermColours = html(Name)-ArgColours,
 1513        (   layout(Name, _, empty)
 1514        ->  attr_colours(One, ArgColours)
 1515        ;   html_colours(One, Colours),
 1516            ArgColours = [Colours]
 1517        )
 1518    ;   Args = [AList,Content]
 1519    ->  TermColours = html(Name)-[AColours, Colours],
 1520        attr_colours(AList, AColours),
 1521        html_colours(Content, Colours)
 1522    ;   TermColours = error
 1523    ).
 1524html_colours(_, classify).
 1525
 1526list_colours(Var, classify) :-
 1527    var(Var),
 1528    !.
 1529list_colours([], []).
 1530list_colours([H0|T0], [H|T]) :-
 1531    !,
 1532    html_colours(H0, H),
 1533    list_colours(T0, T).
 1534list_colours(Last, Colours) :-          % improper list
 1535    html_colours(Last, Colours).
 1536
 1537attr_colours(Var, classify) :-
 1538    var(Var),
 1539    !.
 1540attr_colours([], classify) :- !.
 1541attr_colours(Term, list-Elements) :-
 1542    Term = [_|_],
 1543    !,
 1544    attr_list_colours(Term, Elements).
 1545attr_colours(Name=Value, built_in-[html_attribute(Name), VColour]) :-
 1546    !,
 1547    attr_value_colour(Value, VColour).
 1548attr_colours(NS:Term, built_in-[ html_xmlns(NS),
 1549                                 html_attribute(Name)-[classify]
 1550                               ]) :-
 1551    compound(Term),
 1552    compound_name_arity(Term, Name, 1).
 1553attr_colours(Term, html_attribute(Name)-[VColour]) :-
 1554    compound(Term),
 1555    compound_name_arity(Term, Name, 1),
 1556    !,
 1557    Term =.. [Name,Value],
 1558    attr_value_colour(Value, VColour).
 1559attr_colours(Name, html_attribute(Name)) :-
 1560    atom(Name),
 1561    !.
 1562attr_colours(Term, classify) :-
 1563    compound(Term),
 1564    compound_name_arity(Term, '.', 2),
 1565    !.
 1566attr_colours(_, error).
 1567
 1568attr_list_colours(Var, classify) :-
 1569    var(Var),
 1570    !.
 1571attr_list_colours([], []).
 1572attr_list_colours([H0|T0], [H|T]) :-
 1573    attr_colours(H0, H),
 1574    attr_list_colours(T0, T).
 1575
 1576attr_value_colour(Var, classify) :-
 1577    var(Var).
 1578attr_value_colour(location_by_id(ID), sgml_attr_function-[Colour]) :-
 1579    !,
 1580    location_id(ID, Colour).
 1581attr_value_colour(#(ID), sgml_attr_function-[Colour]) :-
 1582    !,
 1583    location_id(ID, Colour).
 1584attr_value_colour(A+B, sgml_attr_function-[CA,CB]) :-
 1585    !,
 1586    attr_value_colour(A, CA),
 1587    attr_value_colour(B, CB).
 1588attr_value_colour(encode(_), sgml_attr_function-[classify]) :- !.
 1589attr_value_colour(Atom, classify) :-
 1590    atomic(Atom),
 1591    !.
 1592attr_value_colour([_|_], classify) :- !.
 1593attr_value_colour(_Fmt-_Args, classify) :- !.
 1594attr_value_colour(Term, classify) :-
 1595    compound(Term),
 1596    compound_name_arity(Term, '.', 2),
 1597    !.
 1598attr_value_colour(_, error).
 1599
 1600location_id(ID, classify) :-
 1601    var(ID),
 1602    !.
 1603location_id(ID, Class) :-
 1604    (   catch(http_location_by_id(ID, Location), _, fail)
 1605    ->  Class = http_location_for_id(Location)
 1606    ;   Class = http_no_location_for_id(ID)
 1607    ).
 1608location_id(_, classify).
 1609
 1610format_colours(Format, format_string) :- atom(Format), !.
 1611format_colours(Format, format_string) :- string(Format), !.
 1612format_colours(_Format, type_error(text)).
 1613
 1614format_arg_colours(Args, _Format, classify) :- is_list(Args), !.
 1615format_arg_colours(_, _, type_error(list)).
 1616
 1617:- op(990, xfx, :=).                    % allow compiling without XPCE
 1618:- op(200, fy, @). 1619
 1620prolog_colour:style(html(_),                    [colour(magenta4), bold(true)]).
 1621prolog_colour:style(entity(_),                  [colour(magenta4)]).
 1622prolog_colour:style(html_attribute(_),          [colour(magenta4)]).
 1623prolog_colour:style(html_xmlns(_),              [colour(magenta4)]).
 1624prolog_colour:style(format_string(_),           [colour(magenta4)]).
 1625prolog_colour:style(sgml_attr_function,         [colour(blue)]).
 1626prolog_colour:style(http_location_for_id(_),    [bold(true)]).
 1627prolog_colour:style(http_no_location_for_id(_), [colour(red), bold(true)]).
 1628
 1629
 1630prolog_colour:message(html(Element)) -->
 1631    [ '~w: SGML element'-[Element] ].
 1632prolog_colour:message(entity(Entity)) -->
 1633    [ '~w: SGML entity'-[Entity] ].
 1634prolog_colour:message(html_attribute(Attr)) -->
 1635    [ '~w: SGML attribute'-[Attr] ].
 1636prolog_colour:message(sgml_attr_function) -->
 1637    [ 'SGML Attribute function'-[] ].
 1638prolog_colour:message(http_location_for_id(Location)) -->
 1639    [ 'ID resolves to ~w'-[Location] ].
 1640prolog_colour:message(http_no_location_for_id(ID)) -->
 1641    [ '~w: no such ID'-[ID] ].
 1642
 1643
 1644%       prolog:called_by(+Goal, -Called)
 1645%
 1646%       Hook into library(pce_prolog_xref).  Called is a list of callable
 1647%       or callable+N to indicate (DCG) arglist extension.
 1648
 1649
 1650prolog:called_by(Goal, Called) :-
 1651    html_meta_head(Goal, _Module, Head),
 1652    html_meta_called(Head, Goal, Called).
 1653
 1654called_by(Term) -->
 1655    called_by(Term, _).
 1656
 1657called_by(Var, _) -->
 1658    { var(Var) },
 1659    !,
 1660    [].
 1661called_by(\G, M) -->
 1662    !,
 1663    (   { is_list(G) }
 1664    ->  called_by(G, M)
 1665    ;   {atom(M)}
 1666    ->  [(M:G)+2]
 1667    ;   [G+2]
 1668    ).
 1669called_by([], _) -->
 1670    !,
 1671    [].
 1672called_by([H|T], M) -->
 1673    !,
 1674    called_by(H, M),
 1675    called_by(T, M).
 1676called_by(M:Term, _) -->
 1677    !,
 1678    (   {atom(M)}
 1679    ->  called_by(Term, M)
 1680    ;   []
 1681    ).
 1682called_by(Term, M) -->
 1683    { compound(Term),
 1684      !,
 1685      Term =.. [_|Args]
 1686    },
 1687    called_by(Args, M).
 1688called_by(_, _) -->
 1689    [].
 1690
 1691:- multifile
 1692    prolog:hook/1. 1693
 1694prolog:hook(body(_,_,_)).
 1695prolog:hook(body(_,_,_,_)).
 1696prolog:hook(head(_,_,_)).
 1697prolog:hook(head(_,_,_,_)).
 1698
 1699
 1700                 /*******************************
 1701                 *            MESSAGES          *
 1702                 *******************************/
 1703
 1704:- multifile
 1705    prolog:message/3. 1706
 1707prolog:message(html(expand_failed(What))) -->
 1708    [ 'Failed to translate to HTML: ~p'-[What] ].
 1709prolog:message(html(wrong_encoding(Stream, Enc))) -->
 1710    [ 'XHTML demands UTF-8 encoding; encoding of ~p is ~w'-[Stream, Enc] ].
 1711prolog:message(html(multiple_receivers(Id))) -->
 1712    [ 'html_post//2: multiple receivers for: ~p'-[Id] ].
 1713prolog:message(html(no_receiver(Id))) -->
 1714    [ 'html_post//2: no receivers for: ~p'-[Id] ]