
The theory of mconcat is that it should handle monoids that need to be
summed in some special way. I don't know if anyone actually uses it so,
however. Still, Reid is right that the circular dependency sets a very high
bar.
On Aug 31, 2015 2:47 PM, "Reid Barton"
On Mon, Aug 31, 2015 at 1:54 PM, Fermin Reig
wrote: We could generalise:
mconcat:: [a] -> a mconcat = foldr mappend memtpy
to:
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.
Regards, Reid Barton
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