| -- convententionally, we write: | {- | instance (Myeq a) => Myeq [a] where | myeq (x:xs) (y:ys) = (myeq x y)&&(myeq xs ys) | -} | | instance (Myeq a,Myeq [a]) => Myeq [a] where | myeq (x:xs) (y:ys) = (myeq x y)&&(myeq xs ys) | | | | I want to make the 2nd call of myeq to be of an | instance function from the context instead of a | recursive call. And obviously there is an obvious | cycle in the instances declaration. I don't know why you would possibly want this. So far as I can see from your message, the recursive dictionary you are trying to build is exactly the same as what GHC will build automatically from the "conventional" instance declaration. | I run it in ghc6.0.1, it is reported well-typed, but | when I run it with some arguments, I get a run-time | error. | | Loading package base ... linking ... done. | Compiling Myeq ( Myeq.hs, interpreted ) | Ok, modules loaded: Myeq. | *Myeq> myeq [] [] | | Context reduction stack overflow; size = 21 You must have use -fallow-undecidable-instances, and if you do that, you risk divergence. It's really not clear what you expect to happen. Simon