1 Jan
2012
1 Jan
'12
12:48 a.m.
On Sat, Dec 31, 2011 at 11:09 PM, Kevin Quick
varElem :: forall x . (Show x) => Var -> x varElem (V1 x) = x varElem (V2 x) = x
main = putStrLn . elemStr . varElem $ test
The problem here is that you want the return type to depend on the 'value' of Var, which is not known until runtime. Maybe you can wrap the 'conflicting' return type inside an existential type: data VarWrap = forall x . (Show x) => Wrap x instance Show VarWrap where show (Wrap x) = show x varElem :: Var -> VarWrap varElem (V1 x) = Wrap x varElem (V2 x) = Wrap x You will need an 'ExistentialQuantification' language extension to do this.