[Haskell-cafe] Type families are awesome
lrpalmer at gmail.com
Wed Jan 21 03:35:53 EST 2009
2009/1/21 John Ky <newhoggy at gmail.com>
> *Main> let x = lookup
> *Main> let y = Fx.Data.Map.lookup
> Ambiguous type variable `ma' in the constraint:
> `Fx.Data.Map.MapType ma'
> arising from a use of `Fx.Data.Map.lookup' at <interactive>:1:8-25
> Probable fix: add a type signature that fixes these type variable(s)
I think this is just the monomorphism restriction. Turn it off with
-XNoMonomorphismRestriction, or add a parameter to the binding:
let x k = lookup k
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