/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2009-2025, University of Amsterdam
                              VU University Amsterdam
                              SWI-Prolog Solutions b.v.
    All rights reserved.

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    are met:

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       notice, this list of conditions and the following disclaimer.

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       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
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*/

:- module('$dcg',
          [ dcg_translate_rule/2,       % +Rule, -Clause
            dcg_translate_rule/4,       % +Rule, ?Pos0, -Clause, -Pos
            phrase/2,                   % :Rule, ?Input
            phrase/3,                   % :Rule, ?Input, ?Rest
            call_dcg/3                  % :Rule, ?State0, ?State
          ]).

/** <module> Grammar rule (DCG) compiler

This module provides the  term-expansion  rules   for  DCGs  as  well as
phrase/2,3 and call_dcg/3 for calling DCGs. The original code was copied
from C-Prolog and written by Fernando  Pereira, EDCAAD, Edinburgh, 1984.
Since then many people have modified and extended this code.

DCGs have for a long time been a moving target, notably when it comes to
dealing with cuts and unification delaying   for  calls to non-DCG code.
This has slowly converged. This implementation   attempts  to be closely
compatible to the pending ISO standard for DCGs.
*/

dcg_translate_rule(Rule, Clause) :-
    dcg_translate_rule(Rule, _, Clause, _).

dcg_translate_rule((LP,MNT-->RP), Pos0, Clause, Pos) =>
    Clause = (H:-B0,B1),
    f2_pos(Pos0, PosH0, PosRP0, Pos, PosH, PosRP),
    f2_pos(PosH0, PosLP0, PosMNT0, PosH, PosLP, PosMNT),
    '$current_source_module'(M),
    Qualify = q(M,M,_),
    dcg_extend(LP, PosLP0, S0, SR, H, PosLP),
    dcg_body(RP, PosRP0, Qualify, S0, S1, B0, PosRP),
    dcg_body(MNT, PosMNT0, Qualify, SR, S1, B1, PosMNT).
dcg_translate_rule((LP-->RP), Pos0, Clause, Pos) =>
    Clause = (H:-B),
    f2_pos(Pos0, PosLP0, PosRP0, Pos, PosLP, PosRP),
    dcg_extend(LP, PosLP0, S0, S, H, PosLP),
    '$current_source_module'(M),
    Qualify = q(M,M,_),
    dcg_body(RP, PosRP0, Qualify, S0, S, B, PosRP).
dcg_translate_rule((LP,MNT==>RP), Pos0, Clause, Pos), is_list(MNT) =>
    Clause = (H=>B0,B1),
    f2_pos(Pos0, PosH0, PosRP0, Pos, PosH, PosRP),
    f2_pos(PosH0, PosLP0, PosMNT0, PosH, PosLP, PosMNT),
    '$current_source_module'(M),
    Qualify = q(M,M,_),
    dcg_extend(LP, PosLP0, S0, SR, H, PosLP),
    dcg_body(RP, PosRP0, Qualify, S0, S1, B0, PosRP),
    dcg_body(MNT, PosMNT0, Qualify, SR, S1, B1, PosMNT).
dcg_translate_rule((LP,Grd==>RP), Pos0, Clause, Pos) =>
    Clause = (H,Grd=>B),
    f2_pos(Pos0, PosH0, PosRP0, Pos, PosH, PosRP),
    f2_pos(PosH0, PosLP0, PosGrd, PosH, PosLP, PosGrd),
    dcg_extend(LP, PosLP0, S0, S, H, PosLP),
    '$current_source_module'(M),
    Qualify = q(M,M,_),
    dcg_body(RP, PosRP0, Qualify, S0, S, B, PosRP).
dcg_translate_rule((LP==>RP), Pos0, Clause, Pos) =>
    Clause = (H=>B),
    f2_pos(Pos0, PosLP0, PosRP0, Pos, PosLP, PosRP),
    dcg_extend(LP, PosLP0, S0, S, H, PosLP),
    '$current_source_module'(M),
    Qualify = q(M,M,_),
    dcg_body(RP, PosRP0, Qualify, S0, S, B, PosRP).

%!  dcg_body(:DCG, ?Pos0, +Qualify, ?List, ?Tail, -Goal, -Pos) is det.
%
%   Translate DCG body term.

dcg_body(Var, P0, Q, S, SR, phrase(QVar, S, SR), P) :-
    var(Var),
    !,
    qualify(Q, Var, P0, QVar, P).
dcg_body(M:X, Pos0, q(_,C,_), S, SR, Ct, Pos) :-
    !,
    f2_pos(Pos0, _, XP0, _, _, _),
    dcg_body(X, XP0, q(M,C,Pos0), S, SR, Ct, Pos).
dcg_body([], P0, _, S, SR, S=SR, P) :-         % Terminals
    !,
    dcg_terminal_pos(P0, P).
dcg_body(List, P0, _, S, SR, C, P) :-
    (   List = [_|_]
    ->  !,
        (   is_list(List)
        ->  '$append'(List, SR, OL),        % open the list
            C = (S = OL)
        ;   '$type_error'(list, List)
        )
    ;   string(List)                        % double_quotes = string
    ->  !,
        string_codes(List, Codes),
        '$append'(Codes, SR, OL),
        C = (S = OL)
    ),
    dcg_terminal_pos(P0, P).
dcg_body(!, P0, _, S, SR, (!, SR = S), P) :-
    !,
    dcg_cut_pos(P0, P).
dcg_body({}, P, _, S, S, true, P) :- !.
dcg_body({T}, P0, Q, S, SR, (QT, SR = S), P) :-
    !,
    dcg_bt_pos(P0, P1),
    qualify(Q, T, P1, QT, P).
dcg_body((T,R), P0, Q, S, SR, (Tt, Rt), P) :-
    !,
    f2_pos(P0, PA0, PB0, P, PA, PB),
    dcg_body(T, PA0, Q, S, SR1, Tt, PA),
    dcg_body(R, PB0, Q, SR1, SR, Rt, PB).
dcg_body((T;R), P0, Q, S, SR, (Tt;Rt), P) :-
    !,
    f2_pos(P0, PA0, PB0, P, PA, PB),
    dcg_body(T, PA0, Q, S, S1, T1, PA), or_delay_bind(S, SR, S1, T1, Tt),
    dcg_body(R, PB0, Q, S, S2, R1, PB), or_delay_bind(S, SR, S2, R1, Rt).
dcg_body((T|R), P0, Q, S, SR, (Tt;Rt), P) :-
    !,
    f2_pos(P0, PA0, PB0, P, PA, PB),
    dcg_body(T, PA0, Q, S, S1, T1, PA), or_delay_bind(S, SR, S1, T1, Tt),
    dcg_body(R, PB0, Q, S, S2, R1, PB), or_delay_bind(S, SR, S2, R1, Rt).
dcg_body((C->T), P0, Q, S, SR, (Ct->Tt), P) :-
    !,
    f2_pos(P0, PA0, PB0, P, PA, PB),
    dcg_body(C, PA0, Q, S, SR1, Ct, PA),
    dcg_body(T, PB0, Q, SR1, SR, Tt, PB).
dcg_body((C*->T), P0, Q, S, SR, (Ct*->Tt), P) :-
    !,
    f2_pos(P0, PA0, PB0, P, PA, PB),
    dcg_body(C, PA0, Q, S, SR1, Ct, PA),
    dcg_body(T, PB0, Q, SR1, SR, Tt, PB).
dcg_body((\+ C), P0, Q, S, SR, (\+ Ct, SR = S), P) :-
    !,
    f1_pos(P0, PA0, P, PA),
    dcg_body(C, PA0, Q, S, _, Ct, PA).
dcg_body(T, P0, Q, S, SR, QTt, P) :-
    dcg_extend(T, P0, S, SR, Tt, P1),
    qualify(Q, Tt, P1, QTt, P).

or_delay_bind(S, SR, S1, T, (T, SR=S)) :-
    S1 == S,
    !.
or_delay_bind(_S, SR, SR, T, T).

%!  qualify(+QualifyInfo, +Goal, +Pos0, -QGoal, -Pos) is det.
%
%   @arg QualifyInfo is a term   q(Module,Context,Pos), where Module
%   is the module in which Goal must   be  called and Context is the
%   current source module.

qualify(q(M,C,_), X0, Pos0, X, Pos) :-
    M == C,
    !,
    X = X0,
    Pos = Pos0.
qualify(q(M,_,MP), X, Pos0, M:X, Pos) :-
    dcg_qualify_pos(Pos0, MP, Pos).


%!  dcg_extend(+Head, +Extra1, +Extra2, -NewHead)
%
%   Extend Head with two more arguments (on behalf DCG compilation).
%   The solution below is one option. Using   =..  and append is the
%   alternative. In the current version (5.3.2), the =.. is actually
%   slightly faster, but it creates less garbage.

:- dynamic  dcg_extend_cache/4.
:- volatile dcg_extend_cache/4.

dcg_no_extend([]).
dcg_no_extend([_|_]).
dcg_no_extend({_}).
dcg_no_extend({}).
dcg_no_extend(!).
dcg_no_extend((\+_)).
dcg_no_extend((_,_)).
dcg_no_extend((_;_)).
dcg_no_extend((_|_)).
dcg_no_extend((_->_)).
dcg_no_extend((_*->_)).
dcg_no_extend((_-->_)).

%!  dcg_extend(:Rule, ?Pos0, ?List, ?Tail, -Head, -Pos) is det.
%
%   Extend a non-terminal with the   DCG  difference list List\Tail.
%   The position term is extended as well   to reflect the layout of
%   the created term. The additional variables   are  located at the
%   end of the Rule.

dcg_extend(V, _, _, _, _, _) :-
    var(V),
    !,
    throw(error(instantiation_error,_)).
dcg_extend(M:OldT, Pos0, A1, A2, M:NewT, Pos) :-
    !,
    f2_pos(Pos0, MPos, P0, Pos, MPos, P),
    dcg_extend(OldT, P0, A1, A2, NewT, P).
dcg_extend(OldT, P0, A1, A2, NewT, P) :-
    dcg_extend_cache(OldT, A1, A2, NewT),
    !,
    extended_pos(P0, P).
dcg_extend(OldT, P0, A1, A2, NewT, P) :-
    (   callable(OldT)
    ->  true
    ;   throw(error(type_error(callable,OldT),_))
    ),
    (   dcg_no_extend(OldT)
    ->  throw(error(permission_error(define,dcg_nonterminal,OldT),_))
    ;   true
    ),
    (   compound(OldT)
    ->  compound_name_arity(OldT, Name, Arity),
        compound_name_arity(CopT, Name, Arity)
    ;   CopT = OldT,
        Name = OldT,
        Arity = 0
    ),
    NewArity is Arity+2,
    functor(NewT, Name, NewArity),
    copy_args(1, Arity, CopT, NewT),
    A1Pos is Arity+1,
    A2Pos is Arity+2,
    arg(A1Pos, NewT, A1C),
    arg(A2Pos, NewT, A2C),
    assert(dcg_extend_cache(CopT, A1C, A2C, NewT)),
    OldT = CopT,
    A1C = A1,
    A2C = A2,
    extended_pos(P0, P).

copy_args(I, Arity, Old, New) :-
    I =< Arity,
    !,
    arg(I, Old, A),
    arg(I, New, A),
    I2 is I + 1,
    copy_args(I2, Arity, Old, New).
copy_args(_, _, _, _).


                 /*******************************
                 *        POSITION LOGIC        *
                 *******************************/

extended_pos(Pos0, Pos) :-
    '$expand':extended_pos(Pos0, 2, Pos).
f2_pos(Pos0, A0, B0, Pos, A, B) :- '$expand':f2_pos(Pos0, A0, B0, Pos, A, B).
f1_pos(Pos0, A0, Pos, A) :- '$expand':f1_pos(Pos0, A0, Pos, A).

%!  dcg_bt_pos(?BraceTermPos, -Pos) is det.
%
%   Position transformation for mapping of {G} to (G, S=SR).

dcg_bt_pos(Var, Var) :-
    var(Var),
    !.
dcg_bt_pos(brace_term_position(F,T,P0),
           term_position(F,T,F,F,
                         [ P0,
                           term_position(T,T,T,T,_)
                         ])) :- !.
dcg_bt_pos(Pos, _) :-
    expected_layout(brace_term, Pos).

dcg_cut_pos(Var, Var) :-
    var(Var),
    !.
dcg_cut_pos(F-T, term_position(F,T,F,T,
                               [ F-T,
                                 term_position(T,T,T,T,_)
                               ])).
dcg_cut_pos(Pos, _) :-
    expected_layout(atomic, Pos).

%!  dcg_terminal_pos(+ListPos, -TermPos)

dcg_terminal_pos(Pos, _) :-
    var(Pos),
    !.
dcg_terminal_pos(list_position(F,T,_Elms,_Tail),
                 term_position(F,T,_,_,_)).
dcg_terminal_pos(F-T,
                 term_position(F,T,_,_,_)).
dcg_terminal_pos(string_position(F,T),
                 term_position(F,T,_,_,_)).
dcg_terminal_pos(Pos, _) :-
    expected_layout(terminal, Pos).

%!  dcg_qualify_pos(?TermPos0, ?ModuleCreatingPos, -TermPos)

dcg_qualify_pos(Var, _, _) :-
    var(Var),
    !.
dcg_qualify_pos(Pos,
                term_position(F,T,FF,FT,[MP,_]),
                term_position(F,T,FF,FT,[MP,Pos])) :- !.
dcg_qualify_pos(_, Pos, _) :-
    expected_layout(f2, Pos).

expected_layout(Expected, Found) :-
    '$expand':expected_layout(Expected, Found).


                 /*******************************
                 *       PHRASE INTERFACE       *
                 *******************************/

%!  phrase(:RuleSet, ?List).
%!  phrase(:RuleSet, ?List, ?Rest).
%
%   Interface to DCGs

:- meta_predicate
    phrase(//, ?),
    phrase(//, ?, ?),
    call_dcg(//, ?, ?).
:- noprofile((phrase/2,
              phrase/3,
              call_dcg/3)).
:- '$iso'((phrase/2, phrase/3)).

phrase(RuleSet, Input) :-
    phrase(RuleSet, Input, []).
phrase(RuleSet, Input, Rest) :-
    phrase_input(Input),
    phrase_input(Rest),
    call_dcg(RuleSet, Input, Rest).

call_dcg(RuleSet, Input, Rest) :-
    (   strip_module(RuleSet, M, Plain),
        nonvar(Plain),
        dcg_special(Plain)
    ->  dcg_body(Plain, _, q(M,M,_), S0, S, Body, _),
        Input = S0, Rest = S,
        call(M:Body)
    ;   call(RuleSet, Input, Rest)
    ).

phrase_input(Var) :- var(Var), !.
phrase_input([_|_]) :- !.
phrase_input([]) :- !.
phrase_input(Data) :-
    throw(error(type_error(list, Data), _)).

dcg_special(S) :-
    string(S).
dcg_special((_,_)).
dcg_special((_;_)).
dcg_special((_|_)).
dcg_special((_->_)).
dcg_special(!).
dcg_special({_}).
dcg_special([]).
dcg_special([_|_]).
dcg_special(\+_).