Re: [Haskell-cafe] Type families are awesome

2009/1/21 John Ky

*Main> let x = lookup *Main> let y = Fx.Data.Map.lookup

<interactive>:1:8: 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 Luke