[Haskell-cafe] typeclass question

[Johannes Waldmann]

> | class ToRenderable a b where
> |   toRenderable :: a -> Renderable b
> 
> But the above is, I think, too general for my needs. I don't want
> to be able to generate Renderables of different type b for a single input
> type a.

Sounds like a functional dependency (class ToReadable a b | a -> b )

> Also, MPTC take me out of the world of haskell 98, which I was trying
> to avoid. 

Why. "Everyone does it",
and MPTC will be in Haskell-Prime  (but FD may be not)
http://hackage.haskell.org/trac/haskell-prime/wiki/MultiParamTypeClassesDilemma

J.W.

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