The case for typeclasses:
http://research.microsoft.com/en-us/um/people/simonpj/papers/haskell-retrospective/ECOOP-July09.pdf 
(starting from slide 19)

Compare the desugaring of typeclasses with other desugaring:
http://www.haskellforall.com/2014/10/how-to-desugar-haskell-code.html

This slide deck poses many research questions; many developments since
then, but the gist of these questions remains: OOP's way of
implementing polymorphism dispatch-by-value, as opposed to Haskell's
dispatch-by-type (slides 37--40) has its strong points.