在Haskell中实现tails函数

Question

我正在尝试实现该功能tails.这是我的尝试:

tails' :: [a] -> [[a]]
tails' [] = []
tails' (x:xs) = xs:[[tails' xs]]

我一直遇到编译错误:

Couldn't match expected type ‘a’ with actual type ‘[[a]]’
      ‘a’ is a rigid type variable bound by
          the type signature for tails' :: [a] -> [[a]] at..

我的实施有什么问题？

Answer 1

更换

tails' (x:xs) = xs:[[tails' xs]]

有:

tails' (x:xs) = xs : tails' xs

Answer 2

除了语法类型错误之外，您的实现不正确（符合规范）。对比一下这个...

Prelude> let tails [] = [[]]
Prelude|     tails y@(x:xs) = y:(tails xs)
Prelude|
Prelude> tails "abc"
["abc","bc","c",""]