haskell中的点运算符

Question

我有一个使用点运算符的函数。现在我想写没有点。我该怎么做？

all p = and . map p

是这样吗？

all p = and (map p)

我收到以下错误：

4.hs:8:13:
    Couldn't match expected type `[Bool]'
                with actual type `[a0] -> [b0]'
    In the return type of a call of `map'
    Probable cause: `map' is applied to too few arguments
    In the first argument of `and', namely `(map p)'
    In the expression: and (map p)

Answer 1

删除(.) 需要明确添加点是通过您的函数“穿线”的参数。你想要类似的东西

all p xs = and (map p xs)

Answer 2

看(.)的definition：

f . g  =  \ x -> f (g x)

扩展这个给出

and . (map p)  =  \x -> and ((map p) x)

或

all p x  =  and (map p x)