Merge pull request #11 from garyb/mapmaybe-more-filters

Add mapMaybe functions for Map and Set types, filter for Set types

src/Data/Map.purs

@@ -5,7 +5,7 @@ module Data.Map
 
 import Prelude
 
-import Data.Map.Internal (Map, alter, checkValid, delete, empty, filter, filterKeys, filterWithKey, findMax, findMin, foldSubmap, fromFoldable, fromFoldableWith, insert, isEmpty, isSubmap, lookup, lookupGE, lookupGT, lookupLE, lookupLT, member, pop, showTree, singleton, size, submap, toUnfoldable, toUnfoldableUnordered, union, unionWith, unions, difference, update, values)
+import Data.Map.Internal (Map, alter, checkValid, delete, empty, filter, filterKeys, filterWithKey, findMax, findMin, foldSubmap, fromFoldable, fromFoldableWith, insert, isEmpty, isSubmap, lookup, lookupGE, lookupGT, lookupLE, lookupLT, member, pop, showTree, singleton, size, submap, toUnfoldable, toUnfoldableUnordered, union, unionWith, unions, difference, update, values, mapMaybeWithKey, mapMaybe)
 import Data.Set (Set)
 import Unsafe.Coerce (unsafeCoerce)
 

src/Data/Map/Internal.purs

@@ -38,13 +38,15 @@ module Data.Map.Internal
   , filterWithKey
   , filterKeys
   , filter
+  , mapMaybeWithKey
+  , mapMaybe
   ) where
 
 import Prelude
 
 import Data.Eq (class Eq1)
 import Data.Foldable (foldl, foldMap, foldr, class Foldable)
-import Data.FoldableWithIndex (class FoldableWithIndex)
+import Data.FoldableWithIndex (class FoldableWithIndex, foldrWithIndex)
 import Data.FunctorWithIndex (class FunctorWithIndex, mapWithIndex)
 import Data.List (List(..), (:), length, nub)
 import Data.List.Lazy as LL
@@ -644,3 +646,13 @@ filterKeys predicate = filterWithKey $ const <<< predicate
 -- | on the value fails to hold.
 filter :: forall k v. Ord k => (v -> Boolean) -> Map k v -> Map k v
 filter predicate = filterWithKey $ const predicate
+
+-- | Applies a function to each key/value pair in a map, discarding entries
+-- | where the function returns `Nothing`.
+mapMaybeWithKey :: forall k a b. Ord k => (k -> a -> Maybe b) -> Map k a -> Map k b
+mapMaybeWithKey f = foldrWithIndex (\k a acc → maybe acc (\b -> insert k b acc) (f k a)) empty
+
+-- | Applies a function to each value in a map, discarding entries where the
+-- | function returns `Nothing`.
+mapMaybe :: forall k a b. Ord k => (a -> Maybe b) -> Map k a -> Map k b
+mapMaybe = mapMaybeWithKey <<< const

src/Data/Set.purs

@@ -24,6 +24,8 @@ module Data.Set
   , subset
   , properSubset
   , intersection
+  , filter
+  , mapMaybe
   ) where
 
 import Prelude hiding (map)
@@ -39,7 +41,7 @@ import Data.Foldable (class Foldable, foldMap, foldl, foldr)
 import Data.List (List)
 import Data.List as List
 import Data.Map.Internal as M
-import Data.Maybe (Maybe)
+import Data.Maybe (Maybe, maybe)
 import Data.Ord (class Ord1)
 import Data.Unfoldable (class Unfoldable)
 import Partial.Unsafe (unsafePartial)
@@ -178,3 +180,13 @@ intersection s1 s2 = fromFoldable (ST.run (STArray.empty >>= intersect >>= STArr
         LT -> pure $ Loop {a: l + 1, b: r}
         GT -> pure $ Loop {a: l, b: r + 1}
       else pure $ Done acc
+
+-- | Filter out those values of a set for which a predicate on the value fails
+-- | to hold.
+filter :: forall a. Ord a => (a -> Boolean) -> Set a -> Set a
+filter f (Set s) = Set (M.filterWithKey (\k _ -> f k) s)
+
+-- | Applies a function to each value in a set, discarding entries where the
+-- | function returns `Nothing`.
+mapMaybe :: forall a b. Ord b => (a -> Maybe b) -> Set a -> Set b
+mapMaybe f = foldr (\a acc -> maybe acc (\b -> insert b acc) (f a)) empty

src/Data/Set/NonEmpty.purs

@@ -20,6 +20,8 @@ module Data.Set.NonEmpty
   , subset
   , properSubset
   , intersection
+  , filter
+  , mapMaybe
   ) where
 
 import Prelude hiding (map)
@@ -147,3 +149,13 @@ properSubset (NonEmptySet s1) (NonEmptySet s2) = Set.properSubset s1 s2
 -- | if the sets are disjoint.
 intersection :: forall a. Ord a => NonEmptySet a -> NonEmptySet a -> Maybe (NonEmptySet a)
 intersection (NonEmptySet s1) (NonEmptySet s2) = fromSet (Set.intersection s1 s2)
+
+-- | Filter out those values of a set for which a predicate on the value fails
+-- | to hold.
+filter :: forall a. Ord a => (a -> Boolean) -> NonEmptySet a -> Set a
+filter f (NonEmptySet s) = Set.filter f s
+
+-- | Applies a function to each value in a set, discarding entries where the
+-- | function returns `Nothing`.
+mapMaybe :: forall a b. Ord b => (a -> Maybe b) -> NonEmptySet a -> Set b
+mapMaybe f (NonEmptySet s) = Set.mapMaybe f s