有什么区别++和:在haskell中？

Question

我不明白 -

Prelude> "hi"++"there"
"hithere"
Prelude> "hi":"there"

<interactive>:12:6:
    Couldn't match expected type `[Char]' with actual type `Char'
    Expected type: [[Char]]
      Actual type: [Char]
    In the second argument of `(:)', namely `"there"'
    In the expression: "hi" : "there"
Prelude> 

为什么不回归"hithere"？

Answer 1

类型.在GCHi中试试这个:

Prelude> :t (:)
(:) :: a -> [a] -> [a]
Prelude. :t (++)
(++) :: [a] -> [a] -> [a]

Answer 2

我现在明白了.第一个运算符需要是元素,而不是列表.

所以如果我这样'h':"ithere"做会回来"hithere"