haskell列表差异运算符(\\)去了哪里

Question

我遗漏了什么吗？我似乎没有定义列表差异运算符。。。

$ ghci
GHCi, version 8.6.5: http://www.haskell.org/ghc/  :? for help
Prelude> "Hello World!" \ "ell W"
<interactive>:1:16: error:
Variable not in scope: (\) :: [Char] -> [Char] -> t
Prelude> :t (\)
<interactive>:1:1: error: Variable not in scope: \
Prelude> :type (\)
<interactive>:1:1: error: Variable not in scope: \
Prelude> :type (++)
(++) :: [a] -> [a] -> [a]

它被移走了吗？(如果是的话，我该去哪里看？(

Answer 1

它在Data.List:中

% ghci
GHCi, version 8.4.4: http://www.haskell.org/ghc/  :? for help
Prelude> :t (\)
<interactive>:1:1: error: Variable not in scope: \
Prelude> import Data.List
Prelude Data.List> :t (\)
(\) :: Eq a => [a] -> [a] -> [a]