Merge pull request #50 from LiamGoodacre/master

Add `findMap`

Author: garyb

src/Data/Foldable.purs

@@ -16,6 +16,7 @@ module Data.Foldable
   , elem
   , notElem
   , find
+  , findMap
   , maximum
   , maximumBy
   , minimum
@@ -269,6 +270,13 @@ find p = foldl go Nothing
   go Nothing x | p x = Just x
   go r _ = r
 
+-- | Try to find an element in a data structure which satisfies a predicate mapping.
+findMap :: forall a b f. Foldable f => (a -> Maybe b) -> f a -> Maybe b
+findMap p = foldl go Nothing
+  where
+  go Nothing x = p x
+  go r _ = r
+
 -- | Find the largest element of a structure, according to its `Ord` instance.
 maximum :: forall a f. (Ord a, Foldable f) => f a -> Maybe a
 maximum = maximumBy compare

test/Main.purs

@@ -8,7 +8,7 @@ import Control.Monad.Eff.Console (CONSOLE, log)
 import Data.Bifoldable (class Bifoldable, bifoldl, bifoldr, bifoldMap, bifoldrDefault, bifoldlDefault, bifoldMapDefaultR, bifoldMapDefaultL)
 import Data.Bifunctor (class Bifunctor, bimap)
 import Data.Bitraversable (class Bitraversable, bisequenceDefault, bitraverse, bisequence, bitraverseDefault)
-import Data.Foldable (class Foldable, foldl, foldr, foldMap, foldrDefault, foldlDefault, foldMapDefaultR, foldMapDefaultL, minimumBy, minimum, maximumBy, maximum, find)
+import Data.Foldable (class Foldable, foldl, foldr, foldMap, foldrDefault, foldlDefault, foldMapDefaultR, foldMapDefaultL, minimumBy, minimum, maximumBy, maximum, find, findMap)
 import Data.Function (on)
 import Data.Int (toNumber)
 import Data.Maybe (Maybe(..))
@@ -81,6 +81,10 @@ main = do
   assert $ find (_ == 10) [1, 5, 10] == Just 10
   assert $ find (\x -> x `mod` 2 == 0) [1, 4, 10] == Just 4
 
+  log "Test findMap" *> do
+    let pred x = if x > 5 then Just (x * 100) else Nothing
+    assert $ findMap pred [1, 5, 10, 20] == Just 1000
+
   log "Test maximum"
   assert $ maximum (arrayFrom1UpTo 10) == Just 10