Prolog：将列表的元素限制在一个范围内

Question

是否有任何方法可以将列表的元素限制在一个范围内，而不是使用 between(1, 6, X)？

看起来更像 1-6

Answer 1

您可以使用 库 CLPFD :

:- use_module(library(clpfd)).

constraint_list([]).
constraint_list([H|T]):-H in 1..6 ,label([H]),constraint_list(T).

示例：

?- constraint_list([X1,X2]).
X1 = X2, X2 = 2 ;
X1 = 2,
X2 = 3 ;
X1 = 2,
X2 = 4 ;
X1 = 2,
X2 = 5 ;
X1 = 3,
X2 = 2 ;
X1 = X2, X2 = 3 ;
X1 = 3,
X2 = 4 ;
X1 = 3,
X2 = 5 ;
X1 = 4,
X2 = 2 ;
X1 = 4,
X2 = 3 ;
X1 = X2, X2 = 4 ;
X1 = 4,
X2 = 5 ;
X1 = 5,
X2 = 2 ;
X1 = 5,
X2 = 3 ;
X1 = 5,
X2 = 4 ;
X1 = X2, X2 = 5.

?- L=[1,2,3] ,constraint_list(L).
false.

?- L=[2,2,3] ,constraint_list(L).
L = [2, 2, 3].

?- constraint_list(L).
L = [] ;
L = [2] ;
L = [2, 2] ;
L = [2, 2, 2] ;
L = [2, 2, 2, 2] ;
L = [2, 2, 2, 2, 2] ;
L = [2, 2, 2, 2, 2, 2] ;
L = [2, 2, 2, 2, 2, 2, 2] ;
L = [2, 2, 2, 2, 2, 2, 2, 2] ;
L = [2, 2, 2, 2, 2, 2, 2, 2, 2] ;
L = [2, 2, 2, 2, 2, 2, 2, 2, 2|...] ;
L = [2, 2, 2, 2, 2, 2, 2, 2, 2|...] ;
L = [2, 2, 2, 2, 2, 2, 2, 2, 2|...] ;
L = [2, 2, 2, 2, 2, 2, 2, 2, 2|...] ;
L = [2, 2, 2, 2, 2, 2, 2, 2, 2|...] .
    ... (and goes on)

Answer 2

clpfd 库有一个 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.

当调用 all_between(1,6,[X1,X2,X3]). 时，我们得到：

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

如果我们想遍历元素，我们也可以使用label(L).来赋值：

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

对于 all_between_enumerate(1,2,[X1,X2,X3]). 这会生成：

?- 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，这些也会被考虑在内：

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

Prolog：将列表的元素限制在一个范围内

Prolog: Constraining the elements of a list to be within a range

prolog

range

constraint-programming

clpfd