1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2009-2016, 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('$dcg',
   37          [ dcg_translate_rule/2,       % +Rule, -Clause
   38            dcg_translate_rule/4,       % +Rule, ?Pos0, -Clause, -Pos
   39            phrase/2,                   % :Rule, ?Input
   40            phrase/3,                   % :Rule, ?Input, ?Rest
   41            call_dcg/3                  % :Rule, ?State0, ?State
   42          ]).   43
   44                /********************************
   45                *        GRAMMAR RULES          *
   46                *********************************/
   47
   48/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   49The DCG compiler. The original code was copied from C-Prolog and written
   50by Fernando Pereira, EDCAAD, Edinburgh,  1984.   Since  then many people
   51have modified and extended this code. It's a nice mess now and it should
   52be redone from scratch. I won't be doing   this  before I get a complete
   53spec explaining all an implementor needs to   know  about DCG. I'm a too
   54basic user of this facility myself (though   I  learned some tricks from
   55people reporting bugs :-)
   56
   57The original version contained '$t_tidy'/2  to   convert  ((a,b),  c) to
   58(a,(b,c)), but as the  SWI-Prolog  compiler   doesn't  really  care (the
   59resulting code is simply the same), I've removed that.
   60- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
   61
   62dcg_translate_rule(Rule, Clause) :-
   63    dcg_translate_rule(Rule, _, Clause, _).
   64
   65dcg_translate_rule(((LP,MNT)-->RP), Pos0, (H:-B), Pos) :-
   66    !,
   67    f2_pos(Pos0, PosH0, PosRP0, Pos, PosH, PosRP),
   68    f2_pos(PosH0, PosLP0, PosMNT0, PosH, PosLP, PosMNT),
   69    '$current_source_module'(M),
   70    Qualify = q(M,M,_),
   71    dcg_extend(LP, PosLP0, S0, SR, H, PosLP),
   72    dcg_body(RP, PosRP0, Qualify, S0, S1, B0, PosRP),
   73    dcg_body(MNT, PosMNT0, Qualify, SR, S1, B1, PosMNT),
   74    dcg_optimise((B0,B1),B2,S0),
   75    dcg_optimise(B2,B,SR).
   76dcg_translate_rule((LP-->RP), Pos0, (H:-B), Pos) :-
   77    f2_pos(Pos0, PosLP0, PosRP0, Pos, PosLP, PosRP),
   78    dcg_extend(LP, PosLP0, S0, S, H, PosLP),
   79    '$current_source_module'(M),
   80    Qualify = q(M,M,_),
   81    dcg_body(RP, PosRP0, Qualify, S0, S, B0, PosRP),
   82    dcg_optimise(B0,B,S0).
   83
   84%!  dcg_optimise(+BodyIn, -Body, +S0) is det.
   85%
   86%   Performs the following translations:
   87%
   88%     - a(H,T) :- H = [a,b|T], b(T), ... into
   89%       a([a,b|T0]) :- b(T0, T).
   90%     - a(H,T) :- H = [a,b|T] into
   91%       a([a,b|T0])
   92%
   93%   @arg S0 is the initial input list of the rule.
   94
   95dcg_optimise((S00=X,B), B, S0) :-
   96    S00 == S0,
   97    !,
   98    S0 = X.
   99dcg_optimise(S00=X, B, S0) :-
  100    S00 == S0,
  101    !,
  102    S0 = X,
  103    B = true.
  104dcg_optimise(B, B, _).
  105
  106
  107%!  dcg_body(:DCG, ?Pos0, +Qualify, ?List, ?Tail, -Goal, -Pos) is det.
  108%
  109%   Translate DCG body term.
  110
  111dcg_body(Var, P0, Q, S, SR, phrase(QVar, S, SR), P) :-
  112    var(Var),
  113    !,
  114    qualify(Q, Var, P0, QVar, P).
  115dcg_body(M:X, Pos0, q(_,C,_), S, SR, Ct, Pos) :-
  116    !,
  117    f2_pos(Pos0, _, XP0, _, _, _),
  118    dcg_body(X, XP0, q(M,C,Pos0), S, SR, Ct, Pos).
  119dcg_body([], P0, _, S, SR, S=SR, P) :-         % Terminals
  120    !,
  121    dcg_terminal_pos(P0, P).
  122dcg_body(List, P0, _, S, SR, C, P) :-
  123    (   List = [_|_]
  124    ->  !,
  125        (   is_list(List)
  126        ->  '$append'(List, SR, OL),        % open the list
  127            C = (S = OL)
  128        ;   '$skip_list'(_, List, Tail),
  129            var(Tail)
  130        ->  C = '$append'(List, SR, S)      % TBD: Can be optimized
  131        ;   '$type_error'(list_or_partial_list, List)
  132        )
  133    ;   string(List)                        % double_quotes = string
  134    ->  !,
  135        string_codes(List, Codes),
  136        '$append'(Codes, SR, OL),
  137        C = (S = OL)
  138    ),
  139    dcg_terminal_pos(P0, P).
  140dcg_body(!, P0, _, S, SR, (!, SR = S), P) :-
  141    !,
  142    dcg_cut_pos(P0, P).
  143dcg_body({}, P, _, S, S, true, P) :- !.
  144dcg_body({T}, P0, Q, S, SR, (QT, SR = S), P) :-
  145    !,
  146    dcg_bt_pos(P0, P1),
  147    qualify(Q, T, P1, QT, P).
  148dcg_body((T,R), P0, Q, S, SR, (Tt, Rt), P) :-
  149    !,
  150    f2_pos(P0, PA0, PB0, P, PA, PB),
  151    dcg_body(T, PA0, Q, S, SR1, Tt, PA),
  152    dcg_body(R, PB0, Q, SR1, SR, Rt, PB).
  153dcg_body((T;R), P0, Q, S, SR, (Tt;Rt), P) :-
  154    !,
  155    f2_pos(P0, PA0, PB0, P, PA, PB),
  156    dcg_body(T, PA0, Q, S, S1, T1, PA), or_delay_bind(S, SR, S1, T1, Tt),
  157    dcg_body(R, PB0, Q, S, S2, R1, PB), or_delay_bind(S, SR, S2, R1, Rt).
  158dcg_body((T|R), P0, Q, S, SR, (Tt;Rt), P) :-
  159    !,
  160    f2_pos(P0, PA0, PB0, P, PA, PB),
  161    dcg_body(T, PA0, Q, S, S1, T1, PA), or_delay_bind(S, SR, S1, T1, Tt),
  162    dcg_body(R, PB0, Q, S, S2, R1, PB), or_delay_bind(S, SR, S2, R1, Rt).
  163dcg_body((C->T), P0, Q, S, SR, (Ct->Tt), P) :-
  164    !,
  165    f2_pos(P0, PA0, PB0, P, PA, PB),
  166    dcg_body(C, PA0, Q, S, SR1, Ct, PA),
  167    dcg_body(T, PB0, Q, SR1, SR, Tt, PB).
  168dcg_body((C*->T), P0, Q, S, SR, (Ct*->Tt), P) :-
  169    !,
  170    f2_pos(P0, PA0, PB0, P, PA, PB),
  171    dcg_body(C, PA0, Q, S, SR1, Ct, PA),
  172    dcg_body(T, PB0, Q, SR1, SR, Tt, PB).
  173dcg_body((\+ C), P0, Q, S, SR, (\+ Ct, SR = S), P) :-
  174    !,
  175    f1_pos(P0, PA0, P, PA),
  176    dcg_body(C, PA0, Q, S, _, Ct, PA).
  177dcg_body(T, P0, Q, S, SR, QTt, P) :-
  178    dcg_extend(T, P0, S, SR, Tt, P1),
  179    qualify(Q, Tt, P1, QTt, P).
  180
  181or_delay_bind(S, SR, S1, T, (T, SR=S)) :-
  182    S1 == S,
  183    !.
  184or_delay_bind(_S, SR, SR, T, T).
  185
  186%!  qualify(+QualifyInfo, +Goal, +Pos0, -QGoal, -Pos) is det.
  187%
  188%   @arg QualifyInfo is a term   q(Module,Context,Pos), where Module
  189%   is the module in which Goal must   be  called and Context is the
  190%   current source module.
  191
  192qualify(q(M,C,_), X0, Pos0, X, Pos) :-
  193    M == C,
  194    !,
  195    X = X0,
  196    Pos = Pos0.
  197qualify(q(M,_,MP), X, Pos0, M:X, Pos) :-
  198    dcg_qualify_pos(Pos0, MP, Pos).
  199
  200
  201%!  dcg_extend(+Head, +Extra1, +Extra2, -NewHead)
  202%
  203%   Extend Head with two more arguments (on behalf DCG compilation).
  204%   The solution below is one option. Using   =..  and append is the
  205%   alternative. In the current version (5.3.2), the =.. is actually
  206%   slightly faster, but it creates less garbage.
  207
  208:- dynamic  dcg_extend_cache/4.  209:- volatile dcg_extend_cache/4.  210
  211dcg_no_extend([]).
  212dcg_no_extend([_|_]).
  213dcg_no_extend({_}).
  214dcg_no_extend({}).
  215dcg_no_extend(!).
  216dcg_no_extend((\+_)).
  217dcg_no_extend((_,_)).
  218dcg_no_extend((_;_)).
  219dcg_no_extend((_|_)).
  220dcg_no_extend((_->_)).
  221dcg_no_extend((_*->_)).
  222dcg_no_extend((_-->_)).
  223
  224%!  dcg_extend(:Rule, ?Pos0, ?List, ?Tail, -Head, -Pos) is det.
  225%
  226%   Extend a non-terminal with the   DCG  difference list List\Tail.
  227%   The position term is extended as well   to reflect the layout of
  228%   the created term. The additional variables   are  located at the
  229%   end of the Rule.
  230
  231dcg_extend(V, _, _, _, _, _) :-
  232    var(V),
  233    !,
  234    throw(error(instantiation_error,_)).
  235dcg_extend(M:OldT, Pos0, A1, A2, M:NewT, Pos) :-
  236    !,
  237    f2_pos(Pos0, MPos, P0, Pos, MPos, P),
  238    dcg_extend(OldT, P0, A1, A2, NewT, P).
  239dcg_extend(OldT, P0, A1, A2, NewT, P) :-
  240    dcg_extend_cache(OldT, A1, A2, NewT),
  241    !,
  242    extended_pos(P0, P).
  243dcg_extend(OldT, P0, A1, A2, NewT, P) :-
  244    (   callable(OldT)
  245    ->  true
  246    ;   throw(error(type_error(callable,OldT),_))
  247    ),
  248    (   dcg_no_extend(OldT)
  249    ->  throw(error(permission_error(define,dcg_nonterminal,OldT),_))
  250    ;   true
  251    ),
  252    (   compound(OldT)
  253    ->  compound_name_arity(OldT, Name, Arity),
  254        compound_name_arity(CopT, Name, Arity)
  255    ;   CopT = OldT,
  256        Name = OldT,
  257        Arity = 0
  258    ),
  259    NewArity is Arity+2,
  260    functor(NewT, Name, NewArity),
  261    copy_args(1, Arity, CopT, NewT),
  262    A1Pos is Arity+1,
  263    A2Pos is Arity+2,
  264    arg(A1Pos, NewT, A1C),
  265    arg(A2Pos, NewT, A2C),
  266    assert(dcg_extend_cache(CopT, A1C, A2C, NewT)),
  267    OldT = CopT,
  268    A1C = A1,
  269    A2C = A2,
  270    extended_pos(P0, P).
  271
  272copy_args(I, Arity, Old, New) :-
  273    I =< Arity,
  274    !,
  275    arg(I, Old, A),
  276    arg(I, New, A),
  277    I2 is I + 1,
  278    copy_args(I2, Arity, Old, New).
  279copy_args(_, _, _, _).
  280
  281
  282                 /*******************************
  283                 *        POSITION LOGIC        *
  284                 *******************************/
  285
  286extended_pos(Pos0, Pos) :-
  287    '$expand':extended_pos(Pos0, 2, Pos).
  288f2_pos(Pos0, A0, B0, Pos, A, B) :- '$expand':f2_pos(Pos0, A0, B0, Pos, A, B).
  289f1_pos(Pos0, A0, Pos, A) :- '$expand':f1_pos(Pos0, A0, Pos, A).
  290
  291%!  dcg_bt_pos(?BraceTermPos, -Pos) is det.
  292%
  293%   Position transformation for mapping of {G} to (G, S=SR).
  294
  295dcg_bt_pos(Var, Var) :-
  296    var(Var),
  297    !.
  298dcg_bt_pos(brace_term_position(F,T,P0),
  299           term_position(F,T,F,F,
  300                         [ P0,
  301                           term_position(T,T,T,T,_)
  302                         ])) :- !.
  303dcg_bt_pos(Pos, _) :-
  304    expected_layout(brace_term, Pos).
  305
  306dcg_cut_pos(Var, Var) :-
  307    var(Var),
  308    !.
  309dcg_cut_pos(F-T, term_position(F,T,F,T,
  310                               [ F-T,
  311                                 term_position(T,T,T,T,_)
  312                               ])).
  313dcg_cut_pos(Pos, _) :-
  314    expected_layout(atomic, Pos).
  315
  316%!  dcg_terminal_pos(+ListPos, -TermPos)
  317
  318dcg_terminal_pos(Pos, _) :-
  319    var(Pos),
  320    !.
  321dcg_terminal_pos(list_position(F,T,_Elms,_Tail),
  322                 term_position(F,T,_,_,_)).
  323dcg_terminal_pos(F-T,
  324                 term_position(F,T,_,_,_)).
  325dcg_terminal_pos(Pos, _) :-
  326    expected_layout(terminal, Pos).
  327
  328%!  dcg_qualify_pos(?TermPos0, ?ModuleCreatingPos, -TermPos)
  329
  330dcg_qualify_pos(Var, _, _) :-
  331    var(Var),
  332    !.
  333dcg_qualify_pos(Pos,
  334                term_position(F,T,FF,FT,[MP,_]),
  335                term_position(F,T,FF,FT,[MP,Pos])) :- !.
  336dcg_qualify_pos(_, Pos, _) :-
  337    expected_layout(f2, Pos).
  338
  339expected_layout(Expected, Found) :-
  340    '$expand':expected_layout(Expected, Found).
  341
  342
  343                 /*******************************
  344                 *       PHRASE INTERFACE       *
  345                 *******************************/
  346
  347%!  phrase(:RuleSet, ?List).
  348%!  phrase(:RuleSet, ?List, ?Rest).
  349%
  350%   Interface to DCGs
  351
  352:- meta_predicate
  353    phrase(//, ?),
  354    phrase(//, ?, ?),
  355    call_dcg(//, ?, ?).  356:- noprofile((phrase/2,
  357              phrase/3,
  358              call_dcg/3)).  359:- '$iso'((phrase/2, phrase/3)).  360
  361phrase(RuleSet, Input) :-
  362    phrase(RuleSet, Input, []).
  363phrase(RuleSet, Input, Rest) :-
  364    phrase_input(Input),
  365    phrase_input(Rest),
  366    call_dcg(RuleSet, Input, Rest).
  367
  368call_dcg(RuleSet, Input, Rest) :-
  369    (   strip_module(RuleSet, M, Plain),
  370        nonvar(Plain),
  371        dcg_special(Plain)
  372    ->  dcg_body(Plain, _, q(M,M,_), S0, S, Body, _),
  373        Input = S0, Rest = S,
  374        call(M:Body)
  375    ;   call(RuleSet, Input, Rest)
  376    ).
  377
  378phrase_input(Var) :- var(Var), !.
  379phrase_input([_|_]) :- !.
  380phrase_input([]) :- !.
  381phrase_input(Data) :-
  382    throw(error(type_error(list, Data), _)).
  383
  384dcg_special(S) :-
  385    string(S).
  386dcg_special((_,_)).
  387dcg_special((_;_)).
  388dcg_special((_|_)).
  389dcg_special((_->_)).
  390dcg_special(!).
  391dcg_special({_}).
  392dcg_special([]).
  393dcg_special([_|_]).
  394dcg_special(\+_)