mconcat:: Foldable t => t a -> a
mconcat = foldr mappend memtpy
-- even
-- mconcat = fold
I don't understand the appeal of generalizing the type of a function when the generalization already exists; but in this case it's not a viable option anyways because mconcat is a class method of Monoid, and the definition of the Foldable class already refers to Monoid. Creating a circular dependency of Monoid on Foldable would be a headache best avoided.