list Prolog 类型检查
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Prolog type checking
提问by XBigTK13X
Is there a way to determine the type of an element within a list in Prolog? I know that variables aren't explicitly typed in Prolog, but I need to check whether an element is a number, a specific character, etc. How can this be accomplished?
有没有办法确定 Prolog 中列表中元素的类型？我知道在 Prolog 中没有明确输入变量，但我需要检查元素是否是数字、特定字符等。如何实现？
回答by Giulio Piancastelli
Prolog defines a group of built-in predicates for type testing purposes: var/1, atom/1, integer/1, float/1, atomic/1, compound/1, nonvar/1, number/1, all of them with quite a self-explanatory meaning if you know the data types of the language. For specific characters, you may exploit unification with that character, after checking that the element is not a free variable (otherwise unification is always successful).
Prolog 定义了一组用于类型测试目的的内置谓词：var/1, atom/1, integer/1, float/1, atomic/1, compound/1, nonvar/1, number/1，如果您了解该语言的数据类型，所有这些都具有不言自明的含义。对于特定字符，您可以在检查元素不是自由变量后利用与该字符的统一（否则统一总是成功的）。
回答by nhuthai08
You could try this code:
你可以试试这个代码：
isList([_|_]).
isList([]).
Hope it helps.
希望能帮助到你。
回答by Kevin
回答by Stanislav Trifan
to check list you could try:
要检查列表，您可以尝试：
listing(is_list/1, list_functor/1).
is_list(X) :-
functor(X, F, _),
list_functor(F).
list_functor('.').
list_functor('[]').
