I need help understanding how to express the following:
data (Cls a) => B a = B [a]
data GrB a b = GrB (B a)
instance Graph GrB where ...
In the methods for the instance specification, I need to perform Cls a operations on a. * As shown, the compiler complains that it cannot deduce (Cls a) from the context () on those methods. * I can't redefine the Graph methods to introduce the (Cls a) constraint [reasonable] * If I try to express the constraint as part of the Graph instance: "instance (Cls a) => Graph GrB where ..." then it says it's an ambiguous constraint because 'a' isn't mentioned. * I've tried specifying a functional constraint: "instance (Cls a) => Graph GrB | GrB -> a where ..." but that's not valid for an instance declaration. * I can't include a in the GrB instance: "instance (Cls a) => Graph (GrB a b) where ..." because that's a kind conflict. Suggestions/solutions are appreciated. Thanks! -- -KQ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
