165 lines
5.3 KiB
Prolog
165 lines
5.3 KiB
Prolog
:- module(dcgs,
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[op(1105, xfy, '|'),
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phrase/2,
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phrase/3,
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seq//1,
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seqq//1,
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... //0
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]).
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:- use_module(library(error)).
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:- use_module(library(lists), [append/3, member/2]).
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:- use_module(library(loader), [strip_module/3]).
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load_context(GRBody, Module, GRBody0) :-
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strip_module(GRBody, Module, GRBody0),
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( nonvar(Module) ->
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true
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; prolog_load_context(module, Module) ->
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true
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; true
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).
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:- meta_predicate phrase(2, ?).
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:- meta_predicate phrase(2, ?, ?).
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phrase(GRBody, S0) :-
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phrase(GRBody, S0, []).
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phrase(GRBody, S0, S) :-
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load_context(GRBody, Module, GRBody0),
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( var(GRBody0) ->
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instantiation_error(phrase/3)
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; dcg_body(GRBody0, S0, S, GRBody1, Module) ->
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call(GRBody1)
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; type_error(callable, GRBody0, phrase/3)
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).
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module_call_qualified(M, Call, Call1) :-
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( nonvar(M) -> Call1 = M:Call
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; Call = Call1
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).
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% The same version of the below two dcg_rule clauses, but with module scoping.
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dcg_rule(( M:NonTerminal, Terminals --> GRBody ), ( M:Head :- Body )) :-
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dcg_non_terminal(NonTerminal, S0, S, Head),
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dcg_body(GRBody, S0, S1, Goal1, _),
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dcg_terminals(Terminals, S, S1, Goal2),
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Body = ( Goal1, Goal2 ).
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dcg_rule(( M:NonTerminal --> GRBody ), ( M:Head :- Body )) :-
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NonTerminal \= ( _, _ ),
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dcg_non_terminal(NonTerminal, S0, S, Head),
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dcg_body(GRBody, S0, S, Body, _).
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% This program uses append/3 as defined in the Prolog prologue.
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% Expands a DCG rule into a Prolog rule, when no error condition applies.
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dcg_rule(( NonTerminal, Terminals --> GRBody ), ( Head :- Body )) :-
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dcg_non_terminal(NonTerminal, S0, S, Head),
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dcg_body(GRBody, S0, S1, Goal1, _),
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dcg_terminals(Terminals, S, S1, Goal2),
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Body = ( Goal1, Goal2 ).
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dcg_rule(( NonTerminal --> GRBody ), ( Head :- Body )) :-
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NonTerminal \= ( _, _ ),
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dcg_non_terminal(NonTerminal, S0, S, Head),
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dcg_body(GRBody, S0, S, Body, _).
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dcg_non_terminal(NonTerminal, S0, S, Goal) :-
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NonTerminal =.. NonTerminalUniv,
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append(NonTerminalUniv, [S0, S], GoalUniv),
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Goal =.. GoalUniv.
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dcg_terminals(Terminals, S0, S, S0 = List) :-
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append(Terminals, S, List).
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dcg_body(Var, S0, S, Body, M) :-
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var(Var),
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module_call_qualified(M, Var, Var1),
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Body = phrase(Var1, S0, S).
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dcg_body(GRBody, S0, S, Body, M) :-
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nonvar(GRBody),
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dcg_constr(GRBody),
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dcg_cbody(GRBody, S0, S, Body, M).
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dcg_body(NonTerminal, S0, S, Goal1, M) :-
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nonvar(NonTerminal),
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\+ dcg_constr(NonTerminal),
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NonTerminal \= ( _ -> _ ),
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NonTerminal \= ( \+ _ ),
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module_call_qualified(M, Goal, Goal1),
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dcg_non_terminal(NonTerminal, S0, S, Goal).
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% The following constructs in a grammar rule body
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% are defined in the corresponding subclauses.
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dcg_constr([]). % 7.14.1
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dcg_constr([_|_]). % 7.14.2 - terminal sequence
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dcg_constr(( _, _ )). % 7.14.3 - concatenation
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dcg_constr(( _ ; _ )). % 7.14.4 - alternative
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dcg_constr(( _'|'_ )). % 7.14.6 - alternative
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dcg_constr({_}). % 7.14.7
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dcg_constr(call(_)). % 7.14.8
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dcg_constr(phrase(_)). % 7.14.9
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dcg_constr(!). % 7.14.10
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%% dcg_constr(\+ _). % 7.14.11 - not (existence implementation dep.)
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dcg_constr((_->_)). % 7.14.12 - if-then (existence implementation dep.)
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% The principal functor of the first argument indicates
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% the construct to be expanded.
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dcg_cbody([], S0, S, S0 = S, _M).
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dcg_cbody([T|Ts], S0, S, Goal, _M) :-
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must_be(list, [T|Ts]),
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dcg_terminals([T|Ts], S0, S, Goal).
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dcg_cbody(( GRFirst, GRSecond ), S0, S, ( First, Second ), M) :-
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dcg_body(GRFirst, S0, S1, First, M),
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dcg_body(GRSecond, S1, S, Second, M).
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dcg_cbody(( GREither ; GROr ), S0, S, ( Either ; Or ), M) :-
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\+ subsumes_term(( _ -> _ ), GREither),
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dcg_body(GREither, S0, S, Either, M),
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dcg_body(GROr, S0, S, Or, M).
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dcg_cbody(( GRCond ; GRElse ), S0, S, ( Cond ; Else ), M) :-
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subsumes_term(( _GRIf -> _GRThen ), GRCond),
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dcg_cbody(GRCond, S0, S, Cond, M),
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dcg_body(GRElse, S0, S, Else, M).
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dcg_cbody(( GREither '|' GROr ), S0, S, ( Either ; Or ), M) :-
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dcg_body(GREither, S0, S, Either, M),
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dcg_body(GROr, S0, S, Or, M).
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dcg_cbody({Goal}, S0, S, ( Goal1, S0 = S ), M) :-
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module_call_qualified(M, Goal, Goal1).
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dcg_cbody(call(Cont), S0, S, call(Cont1, S0, S), M) :-
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module_call_qualified(M, Cont, Cont1).
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dcg_cbody(phrase(Body), S0, S, phrase(Body1, S0, S), M) :-
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module_call_qualified(M, Body, Body1).
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dcg_cbody(!, S0, S, ( !, S0 = S ), _M).
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dcg_cbody(\+ GRBody, S0, S, ( \+ phrase(GRBody1,S0,_), S0 = S ), M) :-
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module_call_qualified(M, GRBody, GRBody1).
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dcg_cbody(( GRIf -> GRThen ), S0, S, ( If -> Then ), M) :-
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dcg_body(GRIf, S0, S1, If, M),
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dcg_body(GRThen, S1, S, Then, M).
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user:term_expansion(Term0, Term) :-
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nonvar(Term0),
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dcg_rule(Term0, Term).
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% Describes a sequence
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seq([]) --> [].
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seq([E|Es]) --> [E], seq(Es).
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% Describes a sequence of sequences
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seqq([]) --> [].
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seqq([Es|Ess]) --> seq(Es), seqq(Ess).
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% Describes an arbitrary number of elements
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... --> [] | [_], ... .
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user:goal_expansion(phrase(GRBody, S, S0), GRBody1) :-
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load_context(GRBody, M, GRBody0),
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nonvar(GRBody0),
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catch(dcgs:dcg_body(GRBody0, S, S0, GRBody1, M),
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error(E, must_be/2),
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( GRBody1 = throw(error(E, must_be/2)) )
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).
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user:goal_expansion(phrase(GRBody, S), phrase(GRBody, S, [])).
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