Regarding

...

f:: (Show fa) => fb -> fa f = undefined

g:: (Show ga) => ga -> gb g = undefined

-- h:: (Show fa) => t -> fa h b = f (g (h b))

Simon Peyton-Jones wrote:

so the recursive call has the same type as the main function; so the situation is identical to the case where there is no type signature, and the recursive call is at the same type as the function being defined. ... But giving an explicit type signature for h makes it *more* polymorphic, and that in turn leads to ambiguity in this particular case.

I admit I'm confused: can I compose a type expression that describes the type of h? For example, I plan to document the function h and want to give its type signature. I don't know what to write. We know that "(Show fa) => t -> fa" is not it: it's too polymorphic. Is there any type expression that is polymorphic just enough? Thank you!