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added folding1, ifolding1, and itoNonEmptyOf (fixes #1015) #1057

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added folding1, ifolding1, and itoNonEmptyOf (fixes #1015) #1057

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27 changes: 26 additions & 1 deletion src/Control/Lens/Fold.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,7 @@ module Control.Lens.Fold
-- ** Building Folds
, folding, ifolding
, foldring, ifoldring
, folding1, ifolding1
, folded
, folded64
, unfolded
Expand Down Expand Up @@ -120,7 +121,7 @@ module Control.Lens.Fold
, ifoldlOf'
, ifoldrMOf
, ifoldlMOf
, itoListOf
, itoListOf, itoNonEmptyOf
, elemIndexOf
, elemIndicesOf
, findIndexOf
Expand Down Expand Up @@ -159,6 +160,7 @@ import Control.Monad as Monad
import Control.Monad.Reader
import Control.Monad.State
import Data.CallStack
import Data.Semigroup.Foldable(Foldable1, traverse1_)
import Data.Functor.Apply hiding ((<.))
import Data.Int (Int64)
import Data.List (intercalate)
Expand All @@ -175,6 +177,7 @@ import qualified Data.Semigroup as Semi
-- >>> import Data.Function
-- >>> import Data.List.Lens
-- >>> import Data.List.NonEmpty (NonEmpty (..))
-- >>> import qualified Data.List.NonEmpty as NonEmpty
-- >>> import Debug.SimpleReflect.Expr
-- >>> import Debug.SimpleReflect.Vars as Vars hiding (f,g)
-- >>> import Control.DeepSeq (NFData (..), force)
Expand Down Expand Up @@ -203,10 +206,24 @@ folding :: Foldable f => (s -> f a) -> Fold s a
folding sfa agb = phantom . traverse_ agb . sfa
{-# INLINE folding #-}

-- | construct a Fold1 from a function that produces a Foldable1
--
-- >>> toNonEmptyOf folding1 reverse (1 :| [2,3,4])
-- (4 :| [3,2,1])
folding1 :: Foldable1 f => (s -> f a) -> Fold1 s a
folding1 sfa agb = phantom . traverse1_ agb . sfa
{-# INLINE folding1 #-}

ifolding :: (Foldable f, Indexable i p, Contravariant g, Applicative g) => (s -> f (i, a)) -> Over p g s t a b
ifolding sfa f = phantom . traverse_ (phantom . uncurry (indexed f)) . sfa
{-# INLINE ifolding #-}

-- | Version of ifolding to build an 'IndexedFold1'
ifolding1 :: (Foldable1 f, Indexable i p, Contravariant g, Apply g)
=> (s -> f (i, a)) -> Over p g s t a b
ifolding1 sfa f = phantom . traverse1_ (phantom . uncurry (indexed f)) . sfa
{-# INLINE ifolding1 #-}

-- | Obtain a 'Fold' by lifting 'foldr' like function.
--
-- >>> [1,2,3,4]^..foldring foldr
Expand Down Expand Up @@ -643,6 +660,14 @@ toListOf l = foldrOf l (:) []
toNonEmptyOf :: Getting (NonEmptyDList a) s a -> s -> NonEmpty a
toNonEmptyOf l = flip getNonEmptyDList [] . foldMapOf l (NonEmptyDList #. (:|))

-- | indexed version of 'toNonEmptyOf'
--
-- >>> itoNonEmptyOf traverse1 $ "hello" :| ["world"]
-- (0,"hello") :| [(1,"world")]
itoNonEmptyOf :: IndexedGetting i (NonEmptyDList (i,a)) s a -> s -> NonEmpty (i,a)
itoNonEmptyOf l = flip getNonEmptyDList [] . ifoldMapOf l (\i a -> NonEmptyDList $ ((i,a) :|))
{-# INLINE itoNonEmptyOf #-}

-- | Calls 'pure' on the target of a 'Lens', 'Getter', or 'Iso'.
--
-- Calls 'pure' on the targets of a 'Traversal', 'Fold', or 'Prism', and
Expand Down