prolog - 我如何计算原子 Prolog？

Question

我怎么解决这个问题？？

输入：count_atoms(T,Count)

输出 count_atoms(a(b,c(d,e),f),Count)。计数 = 4 ;

我真的不知道......请你能帮帮我吗？

Answer 1

通过 SWI-Prolog 和递归使用库（聚合）：

count_atoms(T, Count) :-
       atom(T)
    -> Count = 1
    ;  compound(T)
    -> aggregate_all(sum(C), (arg(_, T, A), count_atoms(A, C)), Count)
    ;  Count = 0
    .

测试：

?- count_atoms(a(b,c(1,e),f),Count).
Count = 3.

但我担心这不是您分配的解决方案。对于更基本的东西，您可以使用=..分解任何复合术语并在参数列表上递归。

Answer 2

也许基于堆栈的方法可以提供帮助。您可以编写至少四个辅助谓词，如下所示：

% Increases accumulator if T is atomic + call to count_atoms/6
count_atoms(T, Stack, StackSize, Accumulator, Count) :- ...

% Gets the arity of T if T is compound + call to count_atoms/6
count_atoms(T, Stack, StackSize, Accumulator, Count) :- ...

% Gets Nth subterm of T and puts it on the stack + call to count_atoms/6
count_atoms(T, N, Stack, StackSize, Accumulator, Count) :- ...

% Pops element from stack + call to count_atoms/5
count_atoms(T, _, Stack, StackSize, Accumulator, Count) :- ...

但是您仍然需要一个 count_atoms/2 谓词和一个来停止算法并产生结果。