2009/1/21 John Ky <newhoggy@gmail.com>

*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