[Haskell-cafe] Re: Trying to avoid duplicate instances

Thanks for your detailed input -- I appreciate seeing these rather abstract techniques being applied to specific problems. Tom Nielsen pointed me in the direction of the solution you've supplied, so I should have replied to the list that my question had been addressed. Anyhow, I now have code that looks a little like:

class DummySolidObject flag o class SolidObject o

instance FiniteSolidObject o => DummySolidObject Dummy1 o instance InfiniteSolidObject o => DummySolidObject Dummy2 o instance DummySolidObject d o => SolidObject o

data Dummy1 data Dummy2

Thanks, Eric