Prolog 序言：将列表的元素限制在一个范围内

有没有办法将列表中的元素限制在一个范围内，看起来更像

1-6

，而不是使用

介于（1，6，X）

？

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)

---

clpfd

库有一个谓词，您可以在其中为变量列表指定元素的范围

比如：

在（1,6[X1，X2，X3]）之间调用

all_时。

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，我们也可以使用

标签（L）。

来赋值：

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

对于

枚举（1,2[X1，X2，X3]）之间的所有\u。

这将生成：

?- 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.

如果您已经向变量添加了约束，如

X1#

，那么也会考虑这些约束：

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

？-X1#

我们谈论的是整数还是浮点数？

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