Haskell Foldable Wast

Edward Kmett ekmett at gmail.com
Sun Feb 21 23:50:31 UTC 2016

That leads to a ton of ever MORE nonsensical consequences like not being to
weaken calls to mapM (which uses Traversable) to mapM_(which needs only
Foldable) or doubling the number of combinators we have all over again for
random prescriptive reasons, right after we just starting finally healing
the last source of needless duplication (Applicative not being a superclass
of Monad).


On Sun, Feb 21, 2016 at 7:57 AM, Jeremy <voldermort at hotmail.com> wrote:

> Marcin Mrotek wrote
> > I think that, as far as Foldable is concerned, a tuple is equivalent to
> > Identity, so this instance is indeed useless. However, Foldable is a
> > superclass of Traversable (and it wouldn't make much sense to make these
> > classes unrelated, as one can always define folds with `traverse`), so
> > I've
> > always found it a necessary evil.
> Perhaps the case of tuple is evidence that Foldable should *not* be a
> superclass of Traversable?
> --
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