haskell - 为什么 Haskell monadic 是左结合的？

Question

>>=和 >>运算符都是 infixl 1 .为什么是左结合？

特别是，我观察到等价性:

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

所以 do与固定性定义的自然工作方式不同，这令人惊讶。

Answer 1

>>=肯定是左结合的。

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)

和 >>几乎跟随 >>= ;如果它有另一个固定性，它不仅会像 Lennart 所说的那样让人感到奇怪，而且还会阻止您在链中使用这两个运算符:

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