序言删除:不会删除所有与Element合并的元素 [英] Prolog delete: doesn't delete all elements that unify with Element

问题描述

我对SWI-Prolog的delete/3谓词有疑问. 最简单的方法只是一个简单的例子:

I'm having an issue with SWI-Prolog's delete/3 predicate. The easiest way is just a quick example:

?- delete([(1,1),(1,2),(3,2)], (1,_), List).
List = [(1,2),(3,2)].

我希望(1,2)也将被删除，因为(1,_)与(1,2)统一. SWIPL帮助说:

I would expect (1,2) to also be deleted, since (1,_) unifies with (1,2). The SWIPL help says:

删除同时与Elem统一并与List2统一的List1的所有成员.

Delete all members of List1 that simultaneously unify with Elem and unify the result with List2.

这是为什么?如何删除与(1,_)统一的所有内容?

Why is this and how can I delete everything that unifies with (1,_)?

推荐答案

删除同时与Elem统一的List1的所有成员，并与List2统一结果."

" Delete all members of List1 that simultaneously unify with Elem and unify the result with List2."

(1，X)首先与(1,1)统一.因此，X与1统一，不能与2统一删除(1,2). 因此，问题不在于它不会删除成员的所有；这是因为它不能同时与(1,2)和(1,1)统一 (尝试删除[[((1,1)，(1,2)，(1,1)，(3,2)]，(1，_)，列表).

(1,X) first unifies with (1,1). therefore, X is unified with 1 and cannot be unified with 2 to delete (1,2). so the problem is not that it does not delete all of the members; it's that it doesnt unify simultaneously with (1,2) and (1,1) (try delete([(1,1),(1,2),(1,1),(3,2)],(1,_),List).

顺便说一句，根据 swi-prolog手册:

delete(?List1，?Elem，?List2)
当Lis1以及所有出现的Elem删除结果都在List2中时为true.

delete(?List1, ?Elem, ?List2)
Is true when Lis1, with all occurences of Elem deleted results in List2.

此外，不建议使用delete/3:

also, delete/3 is deprecated:

人们可能想通过多种方式从列表中删除元素以证明其名称合理. 考虑匹配(= vs. ==)，先删除/全部删除，确定性与否.

There are too many ways in which one might want to delete elements from a list to justify the name. Think of matching (= vs. ==), delete first/all, be deterministic or not.

因此，最简单的方法是编写您自己的谓词.像这样:

So the easiest way is to write your own predicate. Something like:

my_delete(Pattern,[Pattern|T],TD):-
   my_delete(Pattern,T,TD).
my_delete(Pattern,[H|T],[H|TD]):-
   my_delete(Pattern,T,TD).

也许?

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