Am 03/08/2015 um 10:05 PM schrieb Tom Ellis:
If you really want the type parameter to be exposed you can use
data ProfOps prof = P { pCount :: forall a. prof a -> Count pFilter :: forall a. (a -> Bool) -> prof a -> prof a pAdd :: forall a. prof a -> prof a }
Actually the above is the only version which works because pFilter mentions a. In that case you need the following package
listProf :: ProfOps [] listProf = P { pCount = length, pFilter = filter, pAdd = (++) }
How would I use this? If I have a listProf and I want to perform pCount, must I then choose the pCount from listProf? Something like pCount listProf aProfile But then my code knows that I am using a list representation, which is the thing I wanted to avoid. I tried to pair the ops with the representation, but this also got me into trouble, because when I e.g. do a pAdd then it gets strange when the two operands do not use the same Ops.