I'm looking at GHC's overlapping instances docs here: http://web.mit.edu/ghc/www/users_guide/type-extensions.html#instance-decls and I've ran into the incoherent instances problem. Basically, I have a "catch all" instance that handles all types in a generic manner using SYB introspection, and then I have type specific instances that specialize behavior for certain types. This works with overlapping instances extension but whenever I take advantage of this functionality from polymorphic functions I run into the incoherent instances. If I enable incoherent instances GHC always picks the general case which seems like the wrong thing to do. What I want it to do is delay comitting to an instance until it's processing a specific invocation of a polymorphic function. All the information is available at compile time but I found no way to do this. Is there a way to get around this problem? Thanks, - Slava.