Prolog:将列表的元素限制在一个范围内

Question

有什么方法可以将列表的元素限制在一个范围内，看起来更像是 1-6 , 而不是使用 between(1, 6, X) ?

Answer 1

clpfd图书馆，有一个 ins/2 谓词，您可以在其中指定 - 对于变量列表 - 元素的范围。

喜欢:

all_between(Low, High, Vars) :-
    Vars ins Low..High.

打电话时 all_between(1,6,[X1,X2,X3]).我们得到:

X1 in 1..6,
X2 in 1..6,
X3 in 1..6.

如果我们想枚举元素，我们可以使用 label(L).同样，分配值:

all_between_enumerate(Low, High, Vars) :-
    Vars ins Low..High,
    label(Vars).

对于 all_between_enumerate(1,2,[X1,X2,X3]).这会产生:

?- all_between_enumerate(1,2,[X1,X2,X3]).
X1 = X2, X2 = X3, X3 = 1 ;
X1 = X2, X2 = 1,
X3 = 2 ;
X1 = X3, X3 = 1,
X2 = 2 ;
X1 = 1,
X2 = X3, X3 = 2 ;
X1 = 2,
X2 = X3, X3 = 1 ;
X1 = X3, X3 = 2,
X2 = 1 ;
X1 = X2, X2 = 2,
X3 = 1 ;
X1 = X2, X2 = X3, X3 = 2.

如果您已经为变量添加了约束，例如 X1 #< X3 ，这些也被考虑在内:

?- X1 #< X3, all_between_enumerate(1,2,[X1,X2,X3]).
X1 = X2, X2 = 1,
X3 = 2 ;
X1 = 1,
X3 = X2, X2 = 2.