在Haskell中重载全局&&运算符无法编译

Question

我有一个hs文件,试图重载&&运算符

(&&)::Bool->Bool->Bool
True && x = x
False && _ = False

and' :: (Bool)->Bool
and' xs=foldr (&&) True xs

在Prelude中导入时,出现错误:

Ambiguous occurrence ‘&&’
It could refer to either ‘Main.&&’, defined at D:\baby.hs:2:6
                      or ‘Prelude.&&’,
                         imported from ‘Prelude’ at D:\baby.hs:1:1
                         (and originally defined in ‘GHC.Classes’)

所以我改变了最后一行

and' xs=foldr (Main.&&) True xs

现在它打印新的错误消息:

Couldn't match expected type ‘t0 Bool’ with actual type ‘Bool’
In the third argument of ‘foldr’, namely ‘xs’
In the expression: foldr (Main.&&) True xs

我该如何解决这个问题？谢谢.

Answer 1

正如@zakyggaps在他的评论中所说,(Bool)是一样的Bool.你明确的意思[Bool].此外,您并没有真正"重载"此功能,而是在不同模块中定义类似命名的功能.充满"阴影",但实际上并非如此.