Hey, I ran into this earlier today, though it was in a where clause. :) Luckily I already knew what to google, since there are multiple ways to handle it and I wasn't sure which was best (I went with "just give it a signature"). You're looking at the storied Monomorphism Restriction! https://wiki.haskell.org/Monomorphism_restriction On Tue, Aug 14, 2018, 8:33 PM Jeffrey Brown wrote:

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 synonym:

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 Website https://msu.edu/~brown202/ | Facebook https://www.facebook.com/mejeff.younotjeff | LinkedIn https://www.linkedin.com/in/jeffreybenjaminbrown(spammy, so I often miss messages here) | Github https://github.com/jeffreybenjaminbrown

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