sgml_mode.pl

/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2000-2011, University of Amsterdam
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.

    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in
       the documentation and/or other materials provided with the
       distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.
*/

:- module(emacs_sgml_mode, []).
:- use_module(library(pce)).
:- use_module(library(emacs_extend)).

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
This module exploits the SGML/XML  parser   from  the SWI-Prolog package
sgml2pl to provide syntax colouring for SGML,  XML and HTML modes. Based
on a true parser, we  can  provide   much  better  feedback as heuristic
parsers used in most syntax-driven editors.  For example, we can provide
feedback on SHORTREF matches in  SGML   mode  by highlighting the tokens
acting as a short reference.  We  can   also  easily  give  the scope of
elements that are closed by omited elements.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

:- emacs_begin_mode(sgml, language,
                    "Mode for editing SGML documents",
                    % BINDINGS
                    [ open_document          = button(sgml),
                      reload_dtd             = button(sgml),
                      colourise_buffer       = button(sgml),
                      colourise_and_recenter = key('\\C-l'),
                      tag_selection          = key('\\e,'),
                      colourise_element      = key('\\C-c\\C-s'),
                      forward_move_out       = key('\\ee')
                    ],
                    % SYNTAX TABLE
                    [ '"'  = string_quote('"'),
                      '\'' = string_quote('\''),
                      paragraph_end('\\s *$\\|^<p>\\|\\s +<')
                    ]).

class_variable(auto_colourise_size_limit, int, 100000,
               "Auto-colourise if buffer is smaller then this").

variable(dialect,
         {sgml,xml,html}:=sgml,
         both,
         "?ML Dialect used to parse").
variable(upcase_elements,
         bool := @off,
         both,
         "Upcase inserted elements?").
variable(parser,
         prolog,
         none,
         "Associated (DTD) parser").
variable(auto_colourise_size_limit,
         int,
         both,
         "Auto-colourise if buffer is smaller then this").

%       make_parser(M, Parser)
%
%       Create a parser suitable for the current mode and load the DTD
%       into it.

make_parser(M, Parser) :-
    get(M, dialect, Dialect),
    get(M, text_buffer, TB),
    get(TB, file, File),
    get(File, name, FileName),
    get(M, dialect, Dialect),
    (   Dialect == html
    ->  TheDialect = sgml,
        dtd(html, DTD),
        Options = [dtd(DTD)]
    ;   TheDialect = Dialect,
        Options = []
    ),
    new_sgml_parser(Parser, Options),
    set_sgml_parser(Parser, file(FileName)),
    set_sgml_parser(Parser, dialect(TheDialect)).


%       load_dtd(+Mode, +Parser)
%
%       Load the document DTD into the given parser.

load_dtd(M, _) :-
    get(M, dialect, html),
    !.
load_dtd(M, Parser) :-
    get(M, text_buffer, TB),
    new(Re, regex('<!DOCTYPE', @off)),
    (   send(Re, search, TB)
    ->  get(Re, register_start, Start),
        pce_open(TB, read, In),
        seek(In, Start, bof, _),
        catch(sgml_parse(Parser,
                         [ source(In),
                           parse(declaration)
                         ]),
              E,
              show_message(M, E)),
        close(In)
    ;   send(M, report, warning, 'No <!DOCTYPE declaration')
    ).


parser(M, Reload:[bool], Parser:prolog) :<-
    "Fetch the default parser"::
    (   Reload \== @on,
        get(M, slot, parser, Parser),
        Parser = sgml_parser(_)
    ->  true
    ;   send(M, destroy_dtd),
        make_parser(M, Parser),
        load_dtd(M, Parser),
        send(M, slot, parser, Parser),
        set_sgml_parser(Parser, doctype(_)) % use for partial parsing
    ).


dtd(M, Reload:[bool], DTD:prolog) :<-
    "Fetch the current DTD"::
    get(M, parser, Reload, Parser),
    get_sgml_parser(Parser, dtd(DTD)).


reload_dtd(M) :->
    "Reload the DTD"::
    get(M, dtd, _).


destroy_dtd(M) :->
    "Destroy the associated DTD object"::
    (   get(M, slot, parser, Parser),
        Parser = sgml_parser(_)
    ->  free_sgml_parser(Parser),
        send(M, slot, parser, [])
    ;   true
    ).


                 /*******************************
                 *           INITIALISE         *
                 *******************************/

setup_mode(E) :->
    "Switch editor into fill-mode"::
    send(E, fill_mode, @on).


unlink(M) :->
    send(M, destroy_dtd),
    send_super(M, unlink).


open_document(M, DT:doctype=name) :->
    "Insert <!DOCTYPE line"::
    send(M, format, '<!DOCTYPE %s SYSTEM "">\n\n', DT),
    send(M, backward_char, 4).


                 /*******************************
                 *             HELP             *
                 *******************************/

help_on_mode(M) :->
    (   absolute_file_name(sgml_mode,
                           [ extensions([html]),
                             access(read),
                             file_errors(fail)
                           ],
                           HTML)
    ->  atom_concat('file:', HTML, URI),
        www_open_url(URI)
    ;   send(M, report, warning, 'Can''t find help file')
    ).

                 /*******************************
                 *       RECOULOR POLICIES      *
                 *******************************/

idle(M) :->
    "Idle event was received, colour the current element"::
    send(M, colourise_element, @off).

setup_styles(M) :->
    "Associate defined syntax-styles"::
    (   get(M, attribute, styles_initialised, @on)
    ->  true
    ;   send(M, reload_styles),
        send(M, attribute, styles_initialised, @on)
    ).

set_caret_and_inform(M) :->
    get(M, editor, Editor),
    get(Editor?image, index, @event, Caret),
    send(M, caret, Caret),
    get(M?text_buffer, find_all_fragments,
        message(@arg1, overlap, Caret),
        Fragments),
    send(Fragments, sort, ?(@arg1?length, compare, @arg2?length)),
    get(Fragments, find, ?(@arg1, attribute, balloon), Frag),
    get(Frag, balloon, Balloon),
    send(M, report, warning, 'SGML warning: %s', Balloon).

event(M, Ev:event) :->
    "Show insert-menu on right-down"::
    send(Ev, is_a, ms_right_down),
    (   get(M?image, index, Ev, I)
    ->  send(M, caret, I)
    ;   true
    ),
    send(M, show_menu, Ev).

reload_styles(M) :->
    "Force reloading the styles"::
    (   style_object(Name, Style),
        send(M, style, Name, Style),
        fail
    ;   true
    ).

colourise_element(M, Warn:[bool]) :->
    "Colour element at location"::
    send(M, setup_styles),
    get(M, caret, Caret),
    get(M, text_buffer, TB),
    new(Re, regex('<\\w+')),
    make_parser(M, Parser),
    load_dtd(M, Parser),
    set_sgml_parser(Parser, doctype(_)),
    pce_open(TB, read, In),
    (   get(TB, scan, Caret, line, -2, start, Start),
%           format('Starting from ~w~n', [Start]),
        find_element(M, Parser, Re, In, Start, From-To),
        Caret < To
    ->  send(M, remove_syntax_fragments, From, To),
%           colour_item(element, TB, From, To),
        seek(In, From, bof, _),
        set_sgml_parser(Parser, charpos(From)),
        colourise(M, Parser,
                  [ source(In),
                    parse(element)
                  ])
    ;   Warn == @off
    ->  true
    ;   send(M, report, warning, 'Could not find element')
    ),
    close(In),
    free_sgml_parser(Parser).

%       find_element(+Mode, +Parser, +BeginRegex, +In, +Caret, -From-To)
%
%       Find the start and end of the current element.  We do so by scanning
%       backwards to '<\\w+' (Re).  Then we parse the element and see where
%       it ends.  If this isn't passed the current caret location we look
%       further backward.
%
%       This predicate is non-deterministic, broadening the scope on
%       backtracking.
%
%       By asserting caret/1 before calling this predicate, it will
%       assert a term element(Tag, Attributes, Start, End), where both
%       locations are terms of the form loc(Class, Start, End) indicating
%       the location and type of the begin- and end-tag.

:- dynamic
    caret/1,                        % Caret
    element/4,                      % Tag, Attributes, Start, End
    stack/5.                        % Tag, Attributes, Class, Fro, To

set_caret(Caret) :-
    retractall(caret(Caret)),
    assert(caret(Caret)).

unset_caret :-
    retractall(caret(_)).

find_element(M, Caret, Range) :-
    get(M, parser, Parser),
    get(M, text_buffer, TB),
    pce_open(TB, read, In),
    new(Re, regex('<\\w+')),
    (   find_element(M, Parser, Re, In, Caret, Range)
    ->  close(In)
    ;   close(In),
        fail
    ).

find_element(M, Parser, Re, In, Caret, Range) :-
    get(M, text_buffer, TB),
    send(Re, search, TB, Caret, 0),
    get(Re, register_start, 0, Start0),
    find_element(M, Parser, Re, In, Caret, Start0, Range).

find_element(M, Parser, _Re, In, Caret, Start, Start-To) :-
    \+ get(M?text_buffer, find_fragment,
           and(message(@arg1, overlap, Start),
               @arg1?parsed == @off),
           _),
    seek(In, Start, bof, _),
    set_sgml_parser(Parser, charpos(Start)),
    (   caret(_)
    ->  retractall(element(_,_,_,_)),
        retractall(stack(_,_,_,_,_)),
        Extra = [ call(begin, emacs_sgml_mode:find_on_begin),
                  call(end,   emacs_sgml_mode:find_on_end)
                ]
    ;   Extra = []
    ),
    catch(sgml_parse(Parser,
                     [ source(In),
                       parse(element),
                       syntax_errors(quiet)
                     | Extra
                     ]),
          E,
          show_message(M, E)),
                                    % charpos/1 yields start-position
    get_sgml_parser(Parser, charpos(_, To)),
%       format('Found ~d-~d~n', [Start, To]),
    To-1 > Caret.
find_element(M, Parser, Re, In, Caret, Start0, Range) :-
    get(M, text_buffer, TB),
    send(Re, search, TB, Start0, 0),
    get(Re, register_start, 0, Start1),
    find_element(M, Parser, Re, In, Caret, Start1, Range).

find_on_begin(Tag, Attributes, Parser) :-
    get_sgml_parser(Parser, charpos(From, To)),
    get_sgml_parser(Parser, event_class(Class)),
%       format('BEGIN: ~w ~w-~w (~w)~n', [Tag, From, To, Class]),
    asserta(stack(Tag, Attributes, Class, From, To)).
find_on_end(Tag, Parser) :-
    get_sgml_parser(Parser, charpos(EFrom, ETo)),
%       format('END: ~w ~w-~w~n', [Tag, EFrom, ETo]),
    retract(stack(Tag, Attributes, BClass, BFrom, BTo)),
    caret(Caret),
    (   between(BFrom, ETo, Caret)
    ->  get_sgml_parser(Parser, event_class(EClass)),
        (   element(_,_,_,_)
        ->  true
        ;   assert(element(Tag, Attributes,
                           loc(BClass, BFrom, BTo),
                           loc(EClass, EFrom, ETo)))
        )
    ;   true
    ).


                 /*******************************
                 *         COLOURISING          *
                 *******************************/

colourise_and_recenter(M) :->
    "Colour according to syntax and recenter"::
    send(M, auto_colourise_buffer),
    send(M, recenter).

colourise_buffer(M) :->
    OldTime is cputime,
    new(Class, class(sgml_mode_fragment)),
    get(Class, no_created, OldCreated),

    send(M, setup_styles),
    send(M, remove_syntax_fragments),
    send(M, report, progress, 'Colourising buffer ...'),
    colourise_buffer(M),
    Used is cputime - OldTime,
    get(Class, no_created, NewCreated),
    Created is NewCreated - OldCreated,
    send(M, report, done,
         'done, %.2f seconds, %d fragments', Used, Created).

:- dynamic
    current_tb/2.

colourise_buffer(M) :-
    make_parser(M, Parser),
    get(M, text_buffer, TB),
    pce_open(TB, read, In),
    colourise(M, Parser,
              [ source(In)
              ]),
    free_sgml_parser(Parser).

colourise(M, Parser, Options) :-
    get_sgml_parser(Parser, file(File)),
    get(M, text_buffer, TB),
    asserta(current_tb(TB, File), Ref),
    catch(sgml_parse(Parser,
                     [ call(begin, emacs_sgml_mode:on_begin),
                       call(end,   emacs_sgml_mode:on_end),
                       call(cdata, emacs_sgml_mode:on_cdata),
                       call(decl,  emacs_sgml_mode:on_decl),
                       call(error, emacs_sgml_mode:on_error)
                     | Options
                     ]),
          E,
          show_message(M, E)),
    erase(Ref).

on_begin(_Tag, _Attributes, Parser) :-
    get_sgml_parser(Parser, file(File)),
    current_tb(TB, File),
%       format('Tag ~w, Attr = ~p~n', [Tag, Attributes]),
    get_sgml_parser(Parser, charpos(From, To)),
    get_sgml_parser(Parser, event_class(Class)),
    Class \== omitted,
    colour_item(tag(begin, Class), TB, From, To).
on_end(_Tag, Parser) :-
    get_sgml_parser(Parser, file(File)),
    current_tb(TB, File),
    get_sgml_parser(Parser, charpos(From, To)),
    get_sgml_parser(Parser, event_class(Class)),
%       format('At ~d-~d: Class = ~w~n', [From, To, Class]),
    Class \== omitted,
    colour_item(tag(end, Class), TB, From, To).
on_cdata(_CDATA, Parser) :-
    get_sgml_parser(Parser, file(File)),
    current_tb(TB, File),
    get_sgml_parser(Parser, charpos(From, To)),
    (   get_sgml_parser(Parser, context([Tag|_]))
    ->  (   get_sgml_parser(Parser, dtd(DTD)),
            dtd_property(DTD, element(Tag, _, Model)),
            (   Model == cdata
            ;   Model == rcdata
            )
        ->  Type = cdata
        ;   Type = pcdata
        )
    ),
%       format('CDATA from ~d-~d~n', [From, To]),
    colour_item(cdata(Type), TB, From, To, Fragment),
    (   Type == cdata
    ->  send(Fragment, parsed, @off)
    ;   true
    ).
on_decl(DECL, Parser) :-
    get_sgml_parser(Parser, file(File)),
    current_tb(TB, File),
    get_sgml_parser(Parser, event_class(explicit)),
    get_sgml_parser(Parser, charpos(From, To)),
%       format('Decl ~d-~d: ~w~n', [From, To, DECL]),
    (   DECL == ''
    ->  colour_item(comment, TB, From, To, Fragment),
        send(Fragment, parsed, @off)
    ;   send(regex('DOCTYPE', @off), match, DECL)
    ->  colour_item(doctype, TB, From, To)
    ;   new(Re, regex('\\w*')),
        send(Re, match, DECL),
        get(Re, register_value, DECL, 0, name, DeclType0),
        get(DeclType0, downcase, DeclType),
%           format('Decl(~w)~n', [DeclType]),
        colour_item(decl(DeclType), TB, From, To)
    ).
on_error(Severity, Message, Parser) :-
    current_tb(TB, File),
    (   get_sgml_parser(Parser, file(File))
    ->  get_sgml_parser(Parser, charpos(From, To)),
        colour_item(error(Severity), TB, From, To, Fragment),
        (   Fragment \== @nil
        ->  send(Fragment, message,  Message),
            send(Fragment, severity, Severity)
        ;   true
        )
    ;   format(user_error, 'SGML: Error in other file!~n', [])
    ).

%       colour_item(+Class, +TB, +Pos)
%
%       colourise region if a style is defined for this class.

colour_item(Class, TB, From, To) :-
    colour_item(Class, TB, From, To, _Fragment).

colour_item(Class, TB, From, To, Fragment) :-
    style_name(Class, Name),
    !,
    Len is To - From,
    Len > 0,
    new(Fragment, sgml_mode_fragment(TB, From, Len, Name)).
colour_item(_, _, _, _, @nil).


                 /*******************************
                 *             STYLES           *
                 *******************************/

:- discontiguous
    style_name/2,                   % +Pattern, -StyleName
    style_object/2.                 % +Name, -Style

term_expansion(style(Pattern, Style),
               [ style_name(Pattern, Name),
                 style_object(Name, Style)
               ]) :-
    gensym(syntax_style_, Name).

style(tag(begin, shortref),     style(colour := blue,
                                      background := grey90,
                                      bold   := @on)).
style(tag(begin, _),            style(colour := blue,
                                      bold   := @on)).
style(tag(end, shorttag),       style(colour := blue,
                                      bold   := @on)).
style(tag(end, shortref),       style(colour := blue,
                                      background := grey90,
                                      bold   := @on)).
style(tag(end, _),              style(colour := blue)).
style(cdata(cdata),             style(colour := sea_green)).
style(doctype,                  style(bold := @on)).
style(comment,                  style(colour := dark_green,
                                      background := grey90)).
style(decl(_),                  style(colour := purple)).
style(error(warning),           style(background := orange)).
style(error(_),                 style(background := red)).
style(entity,                   style(colour := dark_green)).
style(element,                  style(background := pale_turquoise)).


                 /*******************************
                 *           TAGGING            *
                 *******************************/

set_insert_point(M, Point:[int]) :->
    "Set mark at point if not set"::
    get(M, mark, Mark),
    (   Mark == 0
    ->  (   Point == @default
        ->  send(M, mark, M?caret)
        ;   send(M, mark, Point)
        )
    ;   true
    ).

insert_begin(M, Tag:name) :->
    "Insert begin-tag and required attributes"::
    fix_case(M, Tag, TheTag),
    send(M, format, '<%s>', TheTag),
    get(M, dtd, DTD),
    findall(A, dtd_property(DTD, attribute(Tag, A, _, required)), List),
    send(M, backward_char),
    insert_attributes(List, M),
    send(M, forward_char).


insert_attributes([], _).
insert_attributes([H|T], M) :-
    send(M, format, ' %s=""', H),
    send(M, set_insert_point, M?caret-1),
    insert_attributes(T, M).


insert_end(M, Tag:name) :->
    "Insert end-tag for element"::
    fix_case(M, Tag, TheTag),
    send(M, format, '</%s>', TheTag).


fix_case(M, Tag, TheTag) :-
    (   get(M, upcase_elements, @on)
    ->  get(Tag, upcase, TheTag)
    ;   TheTag = Tag
    ).


style_for_event(Ev, Style) :-
    (   send(Ev, has_modifier, c)
    ->  Style = inline
    ;   send(Ev, has_modifier, s)
    ->  Style = block
    ;   send(Ev, has_modifier, m)
    ->  Style = shorttag
    ;   Style = @default
    ).


show_menu(M, Ev:event) :->
    "Show menu to insert-tag/tag selection"::
    (   send(M, in_tag)
    ->  send(M, show_attribute_menu, Ev)
    ;   send(M, show_element_menu, Ev)
    ).


in_tag(M) :->
    "Test whether caret is between <>"::
    get(M, caret, Caret),
    get(M, text_buffer, TB),
    send(regex('<[^>]*'), match, TB, Caret, 0),
    send(regex('[^<]*[>/]'), match, TB, Caret). % / for shortag


show_element_menu(M, Ev:event) :->
    "Show menu for inserting a new element"::
    (   get(M, allowed_elements, List),
        delete(List, '#pcdata', Elems),
        Elems \== [],
        sort(Elems, Sorted)
    ->  (   get(M, selection, point(A,B)), B > A
        ->  Label = tag_selection
        ;   Label = insert_element
        ),
        get(Ev, button, Button),
        style_for_event(Ev, Style),
        new(G, popup_gesture(new(P, popup(Label,
                                          message(M, popup_tag_selection,
                                                  @arg1, Style))),
                             Button, new(modifier))),
        send(P, show_label, @on),
        length(Sorted, Len),
        Cols is max(1, Len // 20),
        send(P, columns, Cols),
        send_list(P, append, Sorted),
        send(G, event, Ev)
    ;   send(M, report, warning, 'No element allowed here')
    ).


show_attribute_menu(M, Ev:event) :->
    "Show menu for adding attributes"::
    get(M, caret, Caret),
    get(M, text_buffer, TB),
    new(Re, regex('<[^>]*')),
    send(Re, match, TB, Caret, 0),
    get(Re, register_start, 0, Start),
    (   get(M, looking_at_element, Start, E)
    ->  make_parser(M, Parser),
        load_dtd(M, Parser),
        get_sgml_parser(Parser, dtd(DTD)),
        dtd_property(DTD, attributes(E, Atts)),
        (   Atts == []
        ->  free_sgml_parser(Parser),
            send(M, report, warning, 'Element "%s" has no attributes', E)
        ;   sort(Atts, Sorted),
%               format('Atts = ~p~n', [Sorted]),
            get(Ev, button, Button),
            new(G, popup_gesture(new(P, popup(add_attribute,
                                              message(M, insert_attribute,
                                                      @arg1))),
                                 Button,
                                 new(modifier))),
            send(P, show_label, @on),
            length(Sorted, Len),
            Cols is max(1, Len // 10),
            send(P, columns, Cols),
            fill_attribute_menu(Sorted, DTD, E, P, M),
            free_sgml_parser(Parser),
            send(G, event, Ev)
        )
    ;   send(M, report, warning, 'Not in begin-tag')
    ).


fill_attribute_menu([], _, _, _, _).
fill_attribute_menu([A|T], DTD, E, P, Mode) :-
    dtd_property(DTD, attribute(E, A, Type, Default)),
    add_attribute_menu(Type, Default, A, P, Mode),
    fill_attribute_menu(T, DTD, E, P, Mode).

add_attribute_menu(nameof(List), Def, A, P, Mode) :-
    !,
    send(P, append, new(P2, popup(A, message(Mode, insert_attribute,
                                             A, @arg1)))),
    add_attribute_values(List, Def, P2).
add_attribute_menu(Type, Def, A, P, _Mode) :-
    !,
    type_label(Type, TypeLabel),
    send(P, append, new(MI, menu_item(A, @default,
                                      string('%s (%s)', A, TypeLabel)))),
    (   Def == required
    ->  send(MI, font, bold)
    ;   true
    ).

type_label(list(Type), Label) :-
    !,
    atom_concat(Type, s, Label).
type_label(Type, Type).

add_attribute_values([], _, _).
add_attribute_values([H|T], Def, P) :-
    send(P, append, new(MI, menu_item(H))),
    (   Def == default(H)
    ->  send(MI, font, bold)
    ;   true
    ),
    add_attribute_values(T, Def, P).


insert_attribute(M, Att:name, Val:'[name|int|real]') :->
    "Add attribute-value pair"::
    get(M, text_buffer, TB),
    get(M, caret, Caret),
    new(Re, regex('\\(\\s +\\|[/>]\\)')),
    send(Re, search, TB, Caret),    % find place to insert
    get(Re, register_start, 0, Where),
    (   send(regex('\\s +'), match, TB, Where)
    ->  get(Re, register_end, 0, NewCaret), % after blanks
        send(M, caret, NewCaret)
    ;   send(M, caret, Where),
        send(M, format, ' ')
    ),
    (   Val == @default
    ->  send(M, format, '%s=""', Att),
        get(M, caret, C),
        (   send(M, looking_at, '\\s \\|[/>]')
        ->  true
        ;   send(M, format, ' ')
        ),
        send(M, caret, C-1)
    ;   send(M, format, '%s="%s"', Att, Val),
        (   send(M, looking_at, '\\s \\|[/>]')
        ->  true
        ;   send(M, format, ' ')
        )
    ),
    send(M, mark_undo).             % called from popup!


popup_tag_selection(M, Tag:name, Style0:[{inline,shorttag,block}]) :->
    "->tag_selection wrapper for popup"::
    (   Style0 == @default
    ->  style_for_event(@event, Style)
    ;   Style = Style0
    ),
    send(M, tag_selection, Tag, Style),
    send(M, mark_undo).


tag_selection(M, Tag:[name], Style:[{inline,block,shorttag}]) :->
    "Tag the current selection using element"::
    (   Tag == @default
    ->  new(TI, text_item(element)),
        (   get(M, allowed_elements, List),
%               format('Allowed: ~p~n', [List]),
            delete(List, '#pcdata', Elems),
            sort(Elems, Sorted)
        ->  send(TI, value_set, Sorted)
        ;   true
        ),
        get(M, prompt_using, TI, String),
        get(String, value, TheTag)
    ;   TheTag = Tag
    ),
    (   get(M, selection, point(A,B)),
        B > A
    ->  send(M, tag_region, TheTag, A, B, Style),
        send(M, selection, 0, 0),
        send(M, colourise_element)
    ;   send(M, insert_element, TheTag, Style)
    ).


tag_region(M, Tag:[name], From:int, To:int,
           Style:[{inline,block,shorttag}]) :->
    "Tag a defined region"::
    fix_case(M, Tag, TheTag),
    get(M, text_buffer, TB),
    (   Style == shorttag
    ->  send(TB, insert, To, /),
        send(TB, insert, From, string('<%s/', TheTag))
    ;   Style == block
    ->  (   get(M, column, To, 0)
        ->  send(TB, insert, To, string('</%s>\n', TheTag))
        ;   send(TB, insert, From, string('\n</%s>\n', TheTag))
        ),
        (   get(M, column, From, 0)
        ->  send(TB, insert, From, string('<%s>\n', TheTag))
        ;   send(TB, insert, From, string('\n<%s>\n', TheTag))
        )
    ;   Style == inline
    ->  send(TB, insert, To, string('</%s>', TheTag)),
        send(TB, insert, From, string('<%s>', TheTag))
    ;   get(M, column, From, 0),
        get(M, column, To, 0)
    ->  send(M, tag_region, Tag, From, To, block)
    ;   send(M, tag_region, Tag, From, To, inline)
    ).


insert_element(M, Tag:element=name, Style:[{inline,shorttag,block}]) :->
    "Insert a new empty element"::
    (   get(M, dtd, DTD),
        dtd_property(DTD, element(Tag, Omit, Content))
    ->  true
    ;   Omit = omit(false, false),
        Content = '#pcdata'
    ),
    fix_case(M, Tag, TheTag),
    send(M, prepare_insert),
    send(M, mark, 0),               % put insert position here
    insert_by_style(Style, M, TheTag, Omit, Content, _),
    send(M, colourise_element),
    (   get(M, mark, Mark),
        Mark > 0
    ->  send(M, caret, Mark)
    ;   true
    ).

prepare_insert(M) :->
    "Find location to insert a new tag"::
    get(M, caret, Caret),
    (   find_element(M, Caret, From-_To)
    ->  get(M, looking_at_element, From, E),
%           format('~p: Inserting in "~w" at ~w~n', [M, E, From]),
        get(M, dtd, DTD),
        dtd_property(DTD, element(E, _, Content)),
        (   mixed_content(Content)
        ->  true
        ;   get(M, column, From, Col0),
            Col is Col0+2,
            get(M, text_buffer, TB),
            get(TB, scan, Caret, line, 0, start, SOL),
            (   new(Re, regex('\\s *')),
                send(Re, match, TB, SOL, Caret),
                get(Re, register_end, Caret)
            ->  true                % at a blank line
            ;   send(M, newline)
            ),
            send(M, align_line, Col)
        )
    ;   true
    ).

insert_by_style(_, M, Tag, _, empty, End) :-
    !,
    send(M, insert_begin, Tag),
    (   get(M, dialect, xml)
    ->  send(M, backward_char),
        send(M, format, /),
        send(M, forward_char)
    ;   true
    ),
    get(M, caret, End).
insert_by_style(Style, M, Tag, _, Model, End) :-
    required_content(Model, List),
    (   mixed_content(Model)
    ->  def_style(Style, inline, TheStyle),
        insert_by_style(TheStyle, M, Tag, End),
        send(M, set_insert_point)
    ;   insert_by_style(block, M, Tag, End0),
        get(M, text_buffer, TB),
        new(Mark, fragment(TB, End0, 0)),
        insert_sub_elements(List, M),
        get(Mark, start, End),
        free(Mark)
    ).

mixed_content(M) :-
    term_member('#pcdata', M),
    !.

term_member(X, X).
term_member(X, C) :-
    compound(C),
    arg(_, C, A),
    term_member(X, A).

insert_by_style(shorttag, M, Tag, End) :-
    !,
    send(M, insert_begin, Tag),
    send(M, backward_delete_char),
    send(M, format, '//'),
    get(M, caret, End),
    send(M, backward_char).
insert_by_style(inline, M, Tag, End) :-
    !,
    send(M, insert_begin, Tag),
    get(M, caret, New),
    send(M, insert_end, Tag),
    get(M, caret, End),
    send(M, caret, New).
insert_by_style(block, M, Tag, End) :-
    !,
    send(M, insert_begin, Tag),
    get(M, caret, Insert),
    send(M, newline_and_indent),
    send(M, insert_end, Tag),
    get(M, caret, End),
    send(M, caret, Insert).
insert_by_style(@default, M, Tag, End) :-
    get(M, text_buffer, TB),
    get(M, caret, Caret),
    get(TB, scan, Caret, line, 0, start, SOL),
    (   send(regex('\\s *$'), match, TB, SOL)
    ->  insert_by_style(block, M, Tag, End)
    ;   insert_by_style(inline, M, Tag, End)
    ).


def_style(@default, Style, Style) :- !.
def_style(Style, _, Style).

insert_sub_elements([], _).
insert_sub_elements([H|T], M) :-
    send(M, format, '  '),
    get(M, dtd, DTD),
    dtd_property(DTD, element(H, Omit, Content)),
    send(M, prepare_insert),
    insert_by_style(@default, M, H, Omit, Content, End),
    (   T == []
    ->  true
    ;   send(M, caret, End),
        insert_sub_elements(T, M)
    ).


required_content(empty, []).
required_content(cdata, []).
required_content(Model, Elems) :-
    phrase(required_content(Model), Elems).

required_content((A,B)) -->
    !,
    required_content(A),
    required_content(B).
required_content(&(A,B)) -->
    !,
    required_content(A),
    required_content(B).
required_content('|'(_,_)) -->
    !,
    [].
required_content(?(_)) -->
    [].
required_content(*(_)) -->
    [].
required_content(+(A)) -->
    required_content(A).
required_content('#pcdata') -->
    !,
    [].
required_content(A) -->
    [A].


looking_at_element(M, From:int, Elem:name) :<-
    new(Re, regex('<\\([-_:a-zA-Z0-9]+\\)')),
    get(M, text_buffer, TB),
    send(Re, match, TB, From),
    get(Re, register_value, TB, 1, name, Elem).


allowed_elements(M, Allowed:prolog) :<-
    "Show elements allowed here"::
    get(M, caret, Caret),
    get(M, text_buffer, TB),
    new(Re, regex('<\\w+')),
    make_parser(M, Parser),
    load_dtd(M, Parser),
    get_sgml_parser(Parser, dtd(DTD)),
    set_sgml_parser(Parser, doctype(_)),
    pce_open(TB, read, In),
    set_caret(Caret),
    (   find_element(M, Parser, Re, In, Caret, From-_To),
        get(M, looking_at_element, From, E),
%           format('Looking at ~w~n', [E]),
        (   dtd_property(DTD, doctype(E))
        ;   dtd_property(DTD, element(E, omit(_, false), _))
        )
    ->  unset_caret,
        seek(In, From, bof, _),
        set_sgml_parser(Parser, charpos(From)),
        Len is Caret - From,
        catch(sgml_parse(Parser,
                         [ goal(emacs_sgml_mode:feed(In, Len)),
                           syntax_errors(quiet),
                           parse(input)     % do not complete document
                         ]),
              E,
              show_message(M, E)),
        (   element(_,_,_,loc(explicit,_,_))
        ->  format('End-tag available~n', [])
        ;   true
        ),
        get_sgml_parser(Parser, allowed(Allowed))
    ;   unset_caret,
        dtd_property(DTD, doctype(DocType)),
        atom(DocType)
    ->  Allowed = [DocType]
    ;   send(M, report, warning, 'No current element'),
        Allowed = []
    ),
    close(In),
    free_sgml_parser(Parser).

feed(In, Len, Parser) :-
    copy_stream_data(In, Parser, Len).

report_allowed(M) :->                   % DEBUGGING
    "Report allowed elements at point"::
    get(M, allowed_elements, Allowed),
    atomic_list_concat(Allowed, ', ', Atom),
    send(M, report, status, 'Allowed: %s', Atom).

show_message(M, E) :-
    message_to_string(E, String),
    send(M, report, warning, 'Caught error: %s', String).


                 /*******************************
                 *         MOVING AROUND        *
                 *******************************/

forward_move_out(M) :->
    "Move forwards to end of current element"::
    get(M, caret, Caret),
    (   find_element(M, Caret, _From-To)
    ->  send(M, caret, To)
    ;   send(M, report, warning, 'Cannot find element')
    ).

:- emacs_end_mode.



                 /*******************************
                 *             XML              *
                 *******************************/

:- emacs_begin_mode(xml, sgml,
                    "Mode for editing XML documents",
                    [],
                    []).

initialise(M) :->
    send_super(M, initialise),
    send(M, dialect, xml).

open_document(M, DTD:doctype=name) :->
    "Insert document header"::
    send(M, format, '<?xml version="1.0"?>\n'),
    send_super(M, open_document, DTD).

:- emacs_end_mode.


                 /*******************************
                 *             HTML             *
                 *******************************/

:- emacs_begin_mode(html, sgml,
                    "Mode for editing HTML documents",
                    [],
                    []).

initialise(M) :->
    send_super(M, initialise),
    send(M, dialect, html).

open_document(M) :->
    "Insert document header"::
    send(M, format,
         '<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">\n\n'),
    send(M, insert_element, html).

:- emacs_end_mode.


                 /*******************************
                 *            FRAGMENT          *
                 *******************************/

:- pce_begin_class(sgml_mode_fragment, emacs_colour_fragment,
                   "Provide colourised region").

variable(parsed,   bool := @on,      both, "@off for unparsed fragments").

:- pce_end_class.