[Haskell-cafe] Re: curious about sum

Thomas Davie wrote:

No, I think it's extremely useful. It highlights that numbers can both be lazy and strict, and that the so called "useless" lazy sum, is in fact, useful.

But lazy sum should have beed defined in terms of foldr, not foldl. And foldl is not strict enough for strict sum. Therefore the current choice in the worst of both worlds.