Proposal? foldAlt :: (Foldable t, Alternative f) => t a -> f a

[Andrew Martin]

+1 from me. We probably also want foldMapAlt:

    foldMapAlt :: (Foldable t, Alternative f) => (a -> f b) -> t a -> f b

On Tue, Nov 28, 2017 at 11:12 PM, Fumiaki Kinoshita <fumiexcel at gmail.com>
wrote:

> We found this quite useful, but we are not 100% about the name and
> documentation.
>
> -- | Try—in the 'Alternative' sense—to return all the values in a
> 'Foldable'
> -- container.
> --
> -- @
> -- foldAlt ≡ 'listToMaybe' :: [a] -> 'Maybe' a
> -- foldAlt ≡ 'maybeToList' :: 'Maybe' a -> [a]
> -- foldAlt ≡ 'MaybeT' . 'return' :: ('Monad' m) => 'Maybe' a -> 'MaybeT' m
> a
> -- foldAlt ≡ 'Pipes.ListT' . 'Pipes.each' :: ('Monad' m) => [a] ->
> 'Pipes.ListT' m a
> -- foldAlt ≡ id :: 'Maybe' a -> 'Maybe' a
> -- @
> foldAlt :: (Foldable t, Alternative f) => t a -> f a
> foldAlt = getAlt . foldMap (Alt . pure)
> {-# INLINE foldAlt #-}
>
> I propose adding this to either `Data.Foldable` or `Control.Applicative`.
> Any thoughts?
>
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>


-- 
-Andrew Thaddeus Martin
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