Hi, If I build the code below with -DVER=2, I get a complaint about PatchInspect (PrimOf p) being missing from the context of cleverNamedResolve. This doesn't happen with -DVER=1 or -DVER=3 I presume that type class resolution is operating slightly differently in the different cases, but it's quite confusing - in the original code joinPatches did something useful and I was trying to inline the known instance definition. I would have expected it to be consistent between all three cases, either requiring the context or not. Is it a bug, or just one of the risks one takes by using FlexibleContexts? I've tried this with GHC 6.12.3 and with 7.0.2RC2. Cheers, Ganesh {-# LANGUAGE CPP, TypeFamilies, FlexibleContexts #-} module Class ( cleverNamedResolve ) where data FL p = FL p class PatchInspect p where instance PatchInspect p => PatchInspect (FL p) where type family PrimOf p type instance PrimOf (FL p) = PrimOf p data WithName prim = WithName prim instance PatchInspect prim => PatchInspect (WithName prim) where class (PatchInspect (PrimOf p)) => Conflict p where resolveConflicts :: p -> PrimOf p instance Conflict p => Conflict (FL p) where resolveConflicts = undefined type family OnPrim p #if VER==1 class FromPrims p where instance FromPrims (FL p) where joinPatches :: FromPrims p => p -> p #else #if VER==2 joinPatches :: FL p -> FL p #else joinPatches :: p -> p #endif #endif joinPatches = id cleverNamedResolve :: (Conflict (OnPrim p) ,PrimOf (OnPrim p) ~ WithName (PrimOf p)) => FL (OnPrim p) -> WithName (PrimOf p) cleverNamedResolve = resolveConflicts . joinPatches =============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ===============================================================================