Prolog，将列表拆分为两个列表

Question

我遇到了列表问题。我需要做的是将一个列表 [1,-2,3,-4] 拆分为两个列表 [1,3] 和 [- 2，-4]。我的代码如下所示:

lists([],_,_).
lists([X|Xs],Y,Z):- lists(Xs,Y,Z), X>0 -> append([X],Y,Y) ; append([X],Z,Z).

我得到

Y = [1|Y],
Z = [-2|Z].

我做错了什么？

Answer 1

如果您的 Prolog 系统提供 clpfd你可以保留logical-purity 。想知道怎么做吗？ 继续阅读!

我们采用 lists/3 的第二个定义@CapelliC 写的 his answer作为起点，并替换 partition/4通过 tpartition/4 和(<)/2通过 (#<)/3 :

lists(A,B,C) :- tpartition(#<(0),A,B,C).

让我们运行一个示例查询!

?- As = [0,1,2,-2,3,4,-4,5,6,7,0], lists(As,Bs,Cs).As = [0,1,2,-2,3,4,-4,5,6,7,0],Bs = [  1,2,   3,4,   5,6,7  ],Cs = [0,    -2,    -4,      0].

As we use monotone code, we get logically sound answers for more general queries:

?- As = [X,Y], lists(As,Bs,Cs).
As = [X,Y], Bs = [X,Y], Cs = [   ], X in   1..sup, Y in   1..sup ;
As = [X,Y], Bs = [X  ], Cs = [  Y], X in   1..sup, Y in inf..0   ;
As = [X,Y], Bs = [  Y], Cs = [X  ], X in inf..0  , Y in   1..sup ;
As = [X,Y], Bs = [   ], Cs = [X,Y], X in inf..0  , Y in inf..0   .