Is it really so impossible to implement typeclasses in a way which avoids this problem altogether? Perhaps the need for the MR in the first place is simply an indication that dictionary passing is not a complete solution to implementing typeclasses. It seems quite plausible that there should be an implementation which preserves polymorphism, and yet doesn't result in horrific inefficiency. Do we have a proof (or at least strong evidence) that such a thing can't exist? I'm going to think about this some more. I really find a lot of these solutions to be heavy handed, as you really want things to be polymorphic by default, and let the programmer or various compiler optimisations decide when they're only used monomorphically. A special keyword for killing polymorphic binding might work, but what's so wrong with just adding a type signature? - Cale -- sorry if anyone gets two copies of this, I thought I sent it, but later received notification that it wasn't sent.