[Haskell-cafe] foldl in terms of foldr

[Alexander Solla]

 > f :: a -> b -> c is a function that takes an a, a b, and returns a c.

> Except that f and g are not isomorphic. In fact, there exists no  
> defined fuction g :: (a -> b) -> c
> (what type would (g id) be?

The types are isomorphic.  They both have the same extension.  Both  
types are empty.

How do you make a function that returns an ununtyped value?  You can't.