Haskell Language Fixity declarations Associativity
Example
infixl vs infixr vs infix describe on which sides the parens will be grouped. For example, consider the following fixity declarations (in base)
infixl 6 -
infixr 5 :
infix 4 ==
The infixl tells us that - has left associativity, which means that 1 - 2 - 3 - 4 gets parsed as
((1 - 2) - 3) - 4
The infixr tells us that : has right associativity, which means that 1 : 2 : 3 : [] gets parsed as
1 : (2 : (3 : []))
The infix tells us that == cannot be used without us including parenthesis, which means that True == False == True is a syntax error. On the other hand, True == (False == True) or (True == False) == True are fine.
Operators without an explicit fixity declaration are infixl 9.
