[Haskell-cafe] A function synonym is not (by default) as polymorphic as the original.

Jeffrey Brown jeffbrown.the at gmail.com
Wed Aug 15 03:33:00 UTC 2018

Today I was writing a lot of Hashable instances, and found it hard to read
code littered long lines mostly consisting of `hashWithSalt`, so I made a

infixl 5 ##
(##) = hashWithSalt

But when I replaced all the `hashWithSalt`s with ##, I got lots of weird
errors -- GHC kept wanting things to be Strings that were Ints, or vice
verse. The problem vanished when I added this type signature:

(##) :: Hashable a => Int -> a -> Int

That's exactly the same type signature that hashWithSalt has.

Is this expected behavior? Desirable?

Jeff Brown | Jeffrey Benjamin Brown
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