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1. mapM :: (Traversable t, Monad m) => (a -> m b) -> t a -> m (t b)

   rio	RIO.Prelude

   Map each element of a structure to a monadic action, evaluate these actions from left to right, and collect the results. For a version that ignores the results see mapM_.

   Examples

   mapM is literally a traverse with a type signature restricted to Monad. Its implementation may be more efficient due to additional power of Monad.

2. mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m ()

   rio	RIO.Prelude

   Map each element of a structure to a monadic action, evaluate these actions from left to right, and ignore the results. For a version that doesn't ignore the results see mapM. mapM_ is just like traverse_, but specialised to monadic actions.

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

   rio	RIO.Prelude

   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]
   

4. mapMaybeA :: Applicative f => (a -> f (Maybe b)) -> [a] -> f [b]

   rio	RIO.Prelude

   Applicative mapMaybe.

5. mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]

   rio	RIO.Prelude

   Monadic mapMaybe.

6. mappend :: Monoid a => a -> a -> a

   rio	RIO.Prelude

   An associative operation NOTE: This method is redundant and has the default implementation mappend = (<>) since base-4.11.0.0. Should it be implemented manually, since mappend is a synonym for (<>), it is expected that the two functions are defined the same way. In a future GHC release mappend will be removed from Monoid.

7. mapWithIndex :: (Int -> a -> b) -> Seq a -> Seq b

   rio	RIO.Seq

   A generalization of fmap, mapWithIndex takes a mapping function that also depends on the element's index, and applies it to every element in the sequence.

8. mapMonotonic :: (a -> b) -> Set a -> Set b

   rio	RIO.Set.Unchecked

   The mapMonotonic f s == map f s, but works only when f is strictly increasing. The precondition is not checked. Semi-formally, we have:

   and [x < y ==> f x < f y | x <- ls, y <- ls]
   ==> mapMonotonic f s == map f s
   where ls = toList s
   

9. mapState :: ((a, s) -> (b, s)) -> State s a -> State s b

   rio	RIO.State

   Map both the return value and final state of a computation using the given function.

   • runState (mapState f m) = f . runState
     m

10. mapStateT :: (m (a, s) -> n (b, s)) -> StateT s m a -> StateT s n b

    rio	RIO.State

    Map both the return value and final state of a computation using the given function.

    • runStateT (mapStateT f m) = f .
      runStateT m

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