爲什麼這些表達式具有不同程度的模糊性？

Question

我寫這個函數：

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

我第一次嘗試是一個pointfree實現使用功能組成：

top_ten = take 10 . reverse . sort 

但是這給了以下錯誤：

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 

我的第二次嘗試是一個直截了當的有針對性的實施：

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

這工作，因爲做這些：

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，這些並不：

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) 

究竟是怎麼回事呢？ 什麼導致這些等價表達式具有不同的模糊程度？

Answer 1

根據AndrásKovács在他的評論中所說，Idris無法選擇正確的函數，這取決於您在範圍內的輸入（或函數）。

但是，您可以幫助伊德里斯：

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