Re: [Haskell-cafe] Inferred type not most general?

Greg Buchholz writes:

tmap :: (b -> a, b -> a) -> Twist b b -> Twist a a

...I'm wondering why they couldn't infer the more general...

tmap :: (a -> b, c -> d) -> Twist a c -> Twist b d

Because the latter type involves polymorphic recursion. Standard H-M cannot infer a poly recursive type, but Haskell is willing to check it if you give it a signature. Regards, Malcolm