Prolog 绑定参数 [英] Prolog binding arguments

问题描述

在 sicstus prolog 中，有一个谓词:

In sicstus prolog, there's a predicate:

maplist(:Pred, +List)

Pred 应该只接受一个参数 - List 元素.如何通过定义第一个参数的 2 参数谓词?在其他语言中，它会被写成:

Pred is supposed to take just one argument - List element. How can I pass a 2-argument predicate, with first argument defined? In other languages it would be written as:

maplist(pred.bind(SomeValue), List)

推荐答案

maplist(P_1, Xs) 会为 call(P_1, X) 的每个元素调用 call(P_1, X)代码>Xs.内置谓词call/2 向P_1 添加另一个参数，然后用call/1 调用它.为了表明需要进一步的参数，使用像 P_1 这样的名称非常有帮助，意思是需要一个额外的参数".

maplist(P_1, Xs) will call call(P_1, X) for each element of Xs. The built-in predicate call/2 adds one further argument to P_1 and then calls this with call/1. To indicate that a further argument is needed, it is very helpful to use a name like P_1 meaning "one extra argument is needed".

因此，如果您已经有一个元数为 2 的谓词，例如 (=)/2，您将把 =(2) 传递给 maplist:

So if you have already a predicate of arity 2, say, (=)/2, you will pass =(2) to maplist:

?- maplist(=(2), Xs).
Xs = [] ;
Xs = [2] ;
Xs = [2,2] ...

不幸的是，由于 SICStus 库中的定义不正确，请使用以下定义:

Since the definition in SICStus' library is unfortunately, incorrect, rather use the following definition:

:- meta_predicate(maplist(1,?)).
:- meta_predicate(maplist_i(?,1)).

maplist(P_1, Xs) :-
   maplist_i(Xs, P_1).

maplist_i([], _P_1).
maplist_i([E|Es], P_1) :-
   call(P_1, E),
   maplist_i(Es, P_1).

有关更多信息，请参阅此答案.

See this answer for more.

只是关于列表列表的一个很好的例子.

Just a nice further example about lists of lists.

?- Xss = [[A],[B,C]], maplist(maplist(=(E)), Xss).
Xss = [[E], [E, E]],
A = B, B = C, C = E.

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