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Add foldMapM to Data.Foldable.Extra #119

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Add foldMapM to Data.Foldable.Extra #119

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5 changes: 5 additions & 0 deletions src/Data/Foldable/Extra.hs
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Expand Up @@ -15,6 +15,7 @@ module Data.Foldable.Extra
) where

import Data.Foldable
import Data.Monoid (Ap(..))
import qualified Control.Monad.Extra as MX

-- | Composition of 'not' and 'null'
Expand Down Expand Up @@ -69,3 +70,7 @@ firstJustM p = MX.firstJustM p . toList
-- > compareLength (1:2:3:undefined) 2 == GT
compareLength :: Foldable f => f a -> Int -> Ordering
compareLength = foldr (\_ acc n -> if n > 0 then acc (n - 1) else GT) (compare 0)

-- | A generalization of 'Control.Monad.Extra.concatMapM', 'anyM', 'allM', etc., to an aribtrary 'Monoid'.
foldMapM :: (Foldable f, Applicative m, Monoid b) => (a -> m b) -> f a -> m b
foldMapM f = getAp . foldMap (Ap . f)