Perhaps this ticket is related? http://hackage.haskell.org/trac/ghc/ticket/714
On Thu, Dec 4, 2008 at 9:38 PM, Nicolas Frisby <[EMAIL PROTECTED]> wrote: > From the error below, I'm inferring that the RHS of the associated > type definition can only contain type variables from the instance > head, not the instance context. I didn't explicitly see this > restriction when reading the GHC/Type_families entry. > > Could perhaps the "a b -> bn" functional dependency of the TypeEq > class lift this restriction for bn? This isn't my ball park, but that > idea has my hopes up :). > > <haskell> > {-# LANGUAGE TypeFamilies #-} > > import TypeEq > > -- Attempting to encapsulate TypeEq behind an associated type. > > class EQ a b where > type BN a b > > instance TypeEq a b bn => EQ a b where > type BN a b = bn > </haskell> > > results in an error > > <ghci> > /tmp/Test.hs:9:16: Not in scope: type variable `bn' > Failed, modules loaded: none. > </ghci> > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe