\x -> x + 1

Tour of the Haskell Syntax
http://www.cs.uu.nl/~afie/haskell/tourofsyntax.html
の

Anonymous function can be made using lambda expressions. For example

\x -> x + 1

is a function with one parameter which it will add one to. Lambda expressions prove useful as arguments to for example map:

map (\xs -> zip xs [1..]) list

をやってみる。
まずは\x->x+1。

Prelude List> \x -> x + 1

Top level:
    No instance for (Show (a -> a))
      arising from use of `print' at Top level
    Probable fix: add an instance declaration for (Show (a -> a))
    In a 'do' expression: print it

Showクラスのインスタンスではありません、と・・・
じゃあ、ということで\x -> x + 1 1を実行。

Prelude List> \x -> x + 1 1

Top level:
    No instance for (Show (a -> a))
      arising from use of `print' at Top level
    Probable fix: add an instance declaration for (Show (a -> a))
    In a 'do' expression: print it

:1:10:
    No instance for (Num (t -> a))
      arising from the literal `1' at :1:10
    Probable fix: add an instance declaration for (Num (t -> a))
    In the second argument of `(+)', namely `1 1'
    In a lambda abstraction: \ x -> x + (1 1)
    In the definition of `it': it = \ x -> x + (1 1)

＋が1 1に結合してる？

じゃあ、(\x -> x + 1) 1で！

Prelude List> (\x -> x + 1) 1
2

できた〜