haskell - 为什么Haskell单原子绑定(bind)是左关联的？

>>=和>>运算符都是infixl 1。为什么是左联想？

特别是，我观察到了等效性:

(do a; b; c ) == (a >> (b >> c))   -- Do desugaring
(a >> b >> c) == ((a >> b) >> c)   -- Fixity definition

因此，do与固定性定义自然起作用的方式不同，这令人惊讶。

最佳答案

>>=必须一定是左关联的。

Prelude> ["bla","bli di","blub"] >>= words >>= reverse
"albilbidbulb"
Prelude> ["bla","bli di","blub"] >>= (words >>= reverse)

<interactive>:3:30: error:
    • Couldn't match expected type ‘[[b0]]’
                  with actual type ‘String -> [String]’
    • Probable cause: ‘words’ is applied to too few arguments
      In the first argument of ‘(>>=)’, namely ‘words’
      In the second argument of ‘(>>=)’, namely ‘(words >>= reverse)’
      In the expression:
        ["bla", "bli di", "blub"] >>= (words >>= reverse)

>>几乎跟在>>=之后；如果它具有另一种固定性，不仅会像Lennart所说的那样感到奇怪，还会阻止您在链中同时使用两个运算符:

Prelude> ["bla","bli di","blub"] >>= words >> "Ha"
"HaHaHaHa"
Prelude> infixr 1 ⬿≫; (⬿≫) = (>>)
Prelude> ["bla","bli di","blub"] >>= words ⬿≫ "Ha"

<interactive>:6:1: error:
    Precedence parsing error
        cannot mix ‘>>=’ [infixl 1] and ‘⬿≫’ [infixr 1] in the same infix expression