Hoogle Search

Within LTS Haskell 24.3 (ghc-9.10.2)

Note that Stackage only displays results for the latest LTS and Nightly snapshot. Learn more.

Exact lookup

1. mapMaybe :: forall s a b . (a -> Maybe b) -> IntMap s a -> SomeIntMapWith (SupersetProof 'Int s) b

   refined-containers	Data.IntMap.Refined

   Apply a function to all values in a map and collect only the Just results, returning a potentially smaller map.

2. mapMaybe :: forall s a b . (a -> Maybe b) -> IntMap s a -> SomeIntMapWith (SupersetProof 'Int s) b

   refined-containers	Data.IntMap.Strict.Refined

   Apply a function to all values in a map and collect only the Just results, returning a potentially smaller map.

3. mapMaybe :: forall s k a b . (a -> Maybe b) -> Map s k a -> SomeMapWith (SupersetProof 'Regular s) k b

   refined-containers	Data.Map.Refined

   Apply a function to all values in a map and collect only the Just results, returning a potentially smaller map.

4. mapMaybe :: forall s k a b . (a -> Maybe b) -> Map s k a -> SomeMapWith (SupersetProof 'Regular s) k b

   refined-containers	Data.Map.Strict.Refined

   Apply a function to all values in a map and collect only the Just results, returning a potentially smaller map.

5. mapMaybe :: (a -> Maybe b) -> [a] -> [b]

   verset	Verset

   The mapMaybe function is a version of map which can throw out elements. In particular, the functional argument returns something of type Maybe b. If this is Nothing, no element is added on to the result list. If it is Just b, then b is included in the result list.

   Examples

   Using mapMaybe f x is a shortcut for catMaybes $ map f x in most cases:

   >>> import GHC.Internal.Text.Read ( readMaybe )
   
   >>> let readMaybeInt = readMaybe :: String -> Maybe Int
   
   >>> mapMaybe readMaybeInt ["1", "Foo", "3"]
   [1,3]
   
   >>> catMaybes $ map readMaybeInt ["1", "Foo", "3"]
   [1,3]
   

   If we map the Just constructor, the entire list should be returned:

   >>> mapMaybe Just [1,2,3]
   [1,2,3]
   

6. type family MapMaybe (a1 :: a ~> Maybe b) (a2 :: [a]) :: [b]

   singletons-base	Data.Maybe.Singletons

   No documentation available.

7. mapMaybeMissing :: forall (f :: Type -> Type) x y . Applicative f => (Key -> x -> Maybe y) -> WhenMissing f x y

   containers	Data.IntMap.Internal

   Map over the entries whose keys are missing from the other map, optionally removing some. This is the most powerful SimpleWhenMissing tactic, but others are usually more efficient.

   mapMaybeMissing :: (Key -> x -> Maybe y) -> SimpleWhenMissing x y
   

   mapMaybeMissing f = traverseMaybeMissing (\k x -> pure (f k x))
   

   but mapMaybeMissing uses fewer unnecessary Applicative operations.

8. mapMaybeWithKey :: (Key -> a -> Maybe b) -> IntMap a -> IntMap b

   containers	Data.IntMap.Internal

   Map keys/values and collect the Just results.

   let f k _ = if k < 5 then Just ("key : " ++ (show k)) else Nothing
   mapMaybeWithKey f (fromList [(5,"a"), (3,"b")]) == singleton 3 "key : 3"
   

9. mapMaybeWithKey :: (Key -> a -> Maybe b) -> IntMap a -> IntMap b

   containers	Data.IntMap.Lazy

   Map keys/values and collect the Just results.

   let f k _ = if k < 5 then Just ("key : " ++ (show k)) else Nothing
   mapMaybeWithKey f (fromList [(5,"a"), (3,"b")]) == singleton 3 "key : 3"
   

10. mapMaybeMissing :: forall (f :: Type -> Type) x y . Applicative f => (Key -> x -> Maybe y) -> WhenMissing f x y

    containers	Data.IntMap.Merge.Lazy

    Map over the entries whose keys are missing from the other map, optionally removing some. This is the most powerful SimpleWhenMissing tactic, but others are usually more efficient.

    mapMaybeMissing :: (Key -> x -> Maybe y) -> SimpleWhenMissing x y
    

    mapMaybeMissing f = traverseMaybeMissing (\k x -> pure (f k x))
    

    but mapMaybeMissing uses fewer unnecessary Applicative operations.

Page 13 of many | Previous | Next