Prolog：将列表的元素限制在一个范围内答案

【问题标题】：Prolog: Constraining the elements of a list to be within a rangeProlog：将列表的元素限制在一个范围内
【发布时间】：2017-10-09 04:33:10
【问题描述】：

有没有办法将列表的元素限制在一个范围内，看起来更像1-6，而不是使用between(1, 6, X)？

【问题讨论】：

我们讨论的是整数还是浮点数？

标签： prolog range constraint-programming clpfd

【解决方案1】：

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.

如果我们想枚举元素，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.

【讨论】：

【解决方案2】：

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).

例子：

?- 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)

【讨论】：