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Export specialized folds #40

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25 changes: 20 additions & 5 deletions src/Data/NonEmpty.purs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,10 @@ module Data.NonEmpty
( NonEmpty(..)
, singleton
, (:|)
, fold1
, foldMap1
, foldl1
, foldr1
, fromNonEmpty
, oneOf
, head
Expand All @@ -22,7 +25,7 @@ import Data.FoldableWithIndex (class FoldableWithIndex, foldMapWithIndex, foldlW
import Data.FunctorWithIndex (class FunctorWithIndex, mapWithIndex)
import Data.Maybe (Maybe(..), maybe)
import Data.Ord (class Ord1)
import Data.Semigroup.Foldable (class Foldable1, foldMap1)
import Data.Semigroup.Foldable (class Foldable1, fold1Default)
import Data.Traversable (class Traversable, traverse, sequence)
import Data.TraversableWithIndex (class TraversableWithIndex, traverseWithIndex)
import Data.Tuple (uncurry)
Expand All @@ -46,10 +49,22 @@ infixr 5 NonEmpty as :|
singleton :: forall f a. Plus f => a -> NonEmpty f a
singleton a = a :| empty

-- | Fold a non-empty structure, collecting results using a binary operation.
-- | Fold a non-empty structure, collecting results using a `Semigroup` instance.
fold1 :: forall f m. Foldable f => Semigroup m => NonEmpty f m -> m
fold1 = fold1Default

-- | Fold a non-empty structure by accumulating values in a `Semigroup`.
foldMap1 :: forall f a m. Foldable f => Semigroup m => (a -> m) -> NonEmpty f a -> m
foldMap1 f (a :| fa) = foldl (\s a1 -> s <> f a1) (f a) fa

-- | Fold a non-empty structure from the left, collecting results using a binary operation.
foldl1 :: forall f a. Foldable f => (a -> a -> a) -> NonEmpty f a -> a
foldl1 f (a :| fa) = foldl f a fa

-- | Fold a non-empty structure from the right, collecting results using a binary operation.
foldr1 :: forall f a. Foldable f => (a -> a -> a) -> NonEmpty f a -> a
foldr1 f (a :| fa) = maybe a (f a) $ foldr (\a1 -> Just <<< maybe a1 (f a1)) Nothing fa

fromNonEmpty :: forall f a r. (a -> f a -> r) -> NonEmpty f a -> r
fromNonEmpty f (a :| fa) = a `f` fa

Expand Down Expand Up @@ -105,9 +120,9 @@ instance traversableWithIndexNonEmpty
NonEmpty <$> f Nothing a <*> traverseWithIndex (f <<< Just) fa

instance foldable1NonEmpty :: Foldable f => Foldable1 (NonEmpty f) where
fold1 = foldMap1 identity
foldMap1 f (a :| fa) = foldl (\s a1 -> s <> f a1) (f a) fa
foldr1 f (a :| fa) = maybe a (f a) $ foldr (\a1 -> Just <<< maybe a1 (f a1)) Nothing fa
fold1 = fold1
foldMap1 = foldMap1
foldr1 = foldr1
foldl1 = foldl1

instance unfoldable1NonEmpty :: Unfoldable f => Unfoldable1 (NonEmpty f) where
Expand Down