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Foldable1 instance #27

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Feb 25, 2018
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Foldable1 instance #27

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9 changes: 7 additions & 2 deletions src/Data/NonEmpty.purs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@ import Data.FoldableWithIndex (class FoldableWithIndex, foldMapWithIndex, foldlW
import Data.FunctorWithIndex (class FunctorWithIndex, mapWithIndex)
import Data.Maybe (Maybe(..))
import Data.Ord (class Ord1, compare1)
import Data.Semigroup.Foldable as F1
import Data.Traversable (class Traversable, traverse, sequence)
import Data.TraversableWithIndex (class TraversableWithIndex, traverseWithIndex)

Expand All @@ -50,11 +51,11 @@ foldl1 f (a :| fa) = foldl f a fa

-- | Fold a non-empty structure, collecting results in a `Semigroup`.
foldMap1 :: forall f a s. Semigroup s => Foldable f => (a -> s) -> NonEmpty f a -> s
foldMap1 f (a :| fa) = foldl (\s a1 -> s <> f a1) (f a) fa
foldMap1 = F1.foldMap1

-- | Fold a non-empty structure.
fold1 :: forall f s. Semigroup s => Foldable f => NonEmpty f s -> s
fold1 = foldMap1 id
fold1 = F1.fold1

fromNonEmpty :: forall f a r. (a -> f a -> r) -> NonEmpty f a -> r
fromNonEmpty f (a :| fa) = a `f` fa
Expand Down Expand Up @@ -117,3 +118,7 @@ instance traversableWithIndexNonEmpty
=> TraversableWithIndex (Maybe i) (NonEmpty f) where
traverseWithIndex f (a :| fa) =
NonEmpty <$> f Nothing a <*> traverseWithIndex (f <<< Just) fa

instance foldable1NonEmpty :: Foldable f => F1.Foldable1 (NonEmpty f) where
fold1 = foldMap1 id
foldMap1 f (a :| fa) = foldl (\s a1 -> s <> f a1) (f a) fa