为什么这些表达式具有不同程度的模糊性？

Question

我写这个函数：

||| Returns the ten largest values in the list. 
top_ten : Ord a => List a -> List a 

我第一次尝试是一个pointfree实现使用功能组成：

top_ten = take 10 . reverse . sort 

但是这给了以下错误：

Main.idr:3:9:When checking right hand side of top_ten with expected type 
     List a -> List a 

Can't disambiguate name: Prelude.List.take, Prelude.Stream.take 

我的第二次尝试是一个直截了当的有针对性的实施：

top_ten xs = take 10 (reverse (sort xs)) 

这工作，因为做这些：

top_ten xs = take 10 $ reverse $ sort xs 
top_ten xs = take 10 (reverse $ sort xs) 
top_ten xs = take 10 $ reverse . sort $ xs 
top_ten xs = take 10 (reverse . sort $ xs) 

然而，这些并不：

top_ten xs = take 10 . reverse $ sort xs 
top_ten xs = take 10 . reverse . sort $ xs 
top_ten xs = take 10 $ (reverse . sort) xs 
top_ten xs = (take 10 . reverse) (sort xs) 
top_ten xs = take 10 ((reverse . sort) xs) 

究竟是怎么回事呢？ 什么导致这些等价表达式具有不同的模糊程度？

Answer 1

根据AndrásKovács在他的评论中所说，Idris无法选择正确的函数，这取决于您在范围内的输入（或函数）。

但是，您可以帮助伊德里斯：

top_ten: Ord a => List a -> List a 
top_ten = with Prelude.List take 10 . reverse . sort