在 SWI-Prolog 中实现部分评估

Question

我正在为 Prolog 查询编写部分求值器。我尝试使用 expand_goal/2 扩展查询，但在这种情况下它只是将 Input 与 Output 统一起来：

:- initialization(main).
main :-
    Input=is_between(1,A,3),expand_goal(Input,Output),writeln(Output).
is_between(A,B,C) :- 
    B>A,B<C.

我也试过使用term_expansion/2，但这会导致程序失败：

:- initialization(main).
main :-
    Input=is_between(1,A,3),term_expansion(Input,Output),writeln(Output).
is_between(A,B,C) :- 
    B>A,B<C.

SWI-Prolog 是否有内置谓词可以在运行时执行查询的宏扩展，就像我在这里尝试做的那样？

Answer 1

可以使用内置的 clause/2 predicate. This predicate expands the clause like a hygienic macro:

扩展 Prolog 子句

:- initialization(main).
main :- clause(is_between(1,2,3),B),writeln(B).
is_between(A,B,C) :- A<B,C>B.

此示例打印 1<2,3>2.

可以使用 findall/3 谓词扩展多个子句：

:- initialization(main).
main :- find_all_clauses(is_between(1,2,3),B),writeln(B).

find_all_clauses(Predicate,Output) :-
    findall(Predicate1,clause(Predicate,Predicate1),Output1),
    list_to_disjunction(Output1,Output).

list_to_disjunction([A],A).
list_to_disjunction([A|B],(A;B1)) :- list_to_disjunction(B,B1).

is_between(A,B,C) :- A<B,C>B.
is_between(A,B,C) :- B>A,B<C.

此示例打印 1<2,3>2;2>1,2<3.

我也写了another partial evaluator that expands the goals recursively. There are a few other open-source libraries for partial evaluation in Prolog, such as ecce and logen.

在 SWI-Prolog 中实现部分评估

Implementing partial evaluation in SWI-Prolog

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prolog

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