haskell的一半功能

Question

使用库函数，定义一个函数halve :: [a]→（[a]，[a]） 将一个偶数长度的列表分成两半。例如：

> halve [1, 2, 3, 4, 5, 6] 
([1, 2, 3], [4, 5, 6]) 

到目前为止我有什么是

halve :: [a] -> ([a],[a]) 
halve = (\xs -> case xs of 
     [] -> ([],[]) 
     xs -> take ((length xs) `div` 2) xs) 

，它是错误的，因为XS - >取（（长x）div 2）仅XS显示列表的前半部分..请帮助我继续下去，以便它显示列表的后半部分。

Answer 1

感谢评论一些解决方案。我解决它......这里是

first_halve :: [a] -> [a] 
first_halve = (\xs -> case xs of 
      [] -> [] 
      xs -> take ((length xs) `div` 2) xs) 

second_halve :: [a] -> [a] 
second_halve = (\xs -> case xs of 
      [] -> [] 
      xs -> drop ((length xs) `div` 2) xs) 

halve :: [a] -> ([a],[a]) 
halve = (\xs -> case xs of 
      [] -> ([],[]) 
      xs -> (first_halve xs, second_halve xs))