Prolog递归程序返回的结果太多

Question

我有一个Prolog程序，它是为了找出列表中所有数字的平方和而被三或五整除。然而，它返回多个结果，我不知道为什么。

% --divisibility tests-- 

div_test(N):- 
    % divisible by three? 
    0 is N mod 3. 
div_test(N):- 
    % divisible by five? 
    0 is N mod 5. 

% sum of an empty list is zero (base case) 
square_sum([], Sum):- 
    Sum is 0. 

% --recursive cases 
square_sum([Head | Tail], Sum) :- 
    div_test(Head), 
    square_sum(Tail, TempSum), 
    Sum is Head*Head + TempSum. 

square_sum([Head | Tail], Sum) :- 
    square_sum(Tail, TempSum), 
    Sum is TempSum. 

假定下列输入：

?-square_sum([1,2,3,4,5],Sum). 

我得到以下输出：

Sum = 34 ; 
Sum = 9 ; 
Sum = 25 ; 
Sum = 0. 

34是唯一的输出我应该得到

Answer 1

% --recursive cases 
square_sum([Head | Tail], Sum) :- 
    div_test(Head), 
    square_sum(Tail, TempSum), 
    Sum is Head*Head + TempSum. 

square_sum([Head | Tail], Sum) :- 
    square_sum(Tail, TempSum), 
    Sum is TempSum. 

在第二规则你不测试div_test是否成功编辑。 您可以在第二条规则中，在第一条规则中添加加上剪切后的（！），然后在第一条规则中添加\ + div_test（头部）。

您使用SWI-Prolog的，所以你可以使用模块lambda.pl发现有http://www.complang.tuwien.ac.at/ulrich/Prolog-inedit/lambda.pl写

:- use_module(library(lambda)). 
div_test(N):- 
    % divisible by three? 
    0 is N mod 3. 
div_test(N):- 
    % divisible by five? 
    0 is N mod 5. 

square_sum(Lst, Sum) :- 
    foldl(\X^Y^Z^((div_test(X); div_test(X)) 
       -> Z is Y + X*X 
       ; Z = Y), Lst, 0, Sum).