问题
What is the fixity of backtick operators?
For instance in this code from Real World Haskell:
ghci> (1+) `fmap` [1,2,3] ++ [4,5,6]
[2,3,4,4,5,6]
It's evident the backtick operator `fmap` has a higher fixity than ++, but none is given by GHCi.
回答1:
§4.4.2 of the Haskell Report states that
Any operator lacking a fixity declaration is assumed to be infixl 9
"Any operator" includes normal function names in backticks.
Your example shows that `fmap` does have higher fixity than ++, because ++ acts on the result of the fmap.
来源：https://stackoverflow.com/questions/7807994/fixity-of-backtick-operators