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

   prelude-compat	Prelude2010

   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 ()

   prelude-compat	Prelude2010

   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. mapBoth :: (a -> c) -> (b -> d) -> Either a b -> Either c d

   rebase	Rebase.Prelude

   The mapBoth function takes two functions and applies the first if iff the value takes the form Left _ and the second if the value takes the form Right _. Using Data.Bifunctor:

   mapBoth = bimap
   

   Using Control.Arrow:

   mapBoth = (+++)
   

   >>> mapBoth (*2) (*3) (Left 4)
   Left 8
   

   >>> mapBoth (*2) (*3) (Right 4)
   Right 12
   

4. mapCont :: (r -> r) -> Cont r a -> Cont r a

   rebase	Rebase.Prelude

   Apply a function to transform the result of a continuation-passing computation.

   • runCont (mapCont f m) = f . runCont
     m

5. mapExcept :: (Either e a -> Either e' b) -> Except e a -> Except e' b

   rebase	Rebase.Prelude

   Map the unwrapped computation using the given function.

   • runExcept (mapExcept f m) = f (runExcept
     m)

6. mapExceptT :: (m (Either e a) -> n (Either e' b)) -> ExceptT e m a -> ExceptT e' n b

   rebase	Rebase.Prelude

   Map the unwrapped computation using the given function.

   • runExceptT (mapExceptT f m) = f
     (runExceptT m)

7. mapMaybeT :: (m (Maybe a) -> n (Maybe b)) -> MaybeT m a -> MaybeT n b

   rebase	Rebase.Prelude

   Transform the computation inside a MaybeT.

   • runMaybeT (mapMaybeT f m) = f (runMaybeT
     m)

8. mapReader :: (a -> b) -> Reader r a -> Reader r b

   rebase	Rebase.Prelude

   Transform the value returned by a Reader.

   • runReader (mapReader f m) = f .
     runReader m

9. mapReaderT :: (m a -> n b) -> ReaderT r m a -> ReaderT r n b

   rebase	Rebase.Prelude

   Transform the computation inside a ReaderT.

   • runReaderT (mapReaderT f m) = f .
     runReaderT m

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

    rebase	Rebase.Prelude

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

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

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