haskell2010-1.0.0.0: Control/Monad.hs

-- |
-- The "Control.Monad" module provides the 'Functor', 'Monad' and
-- 'MonadPlus' classes, together with some useful operations on monads.

module Control.Monad (
    -- * Functor and monad classes

      Functor(fmap)
    , Monad((>>=), (>>), return, fail)

    , MonadPlus (   -- class context: Monad
          mzero     -- :: (MonadPlus m) => m a
        , mplus     -- :: (MonadPlus m) => m a -> m a -> m a
        )
    -- * Functions

    -- ** Naming conventions
    -- $naming

    -- ** Basic @Monad@ functions

    , mapM          -- :: (Monad m) => (a -> m b) -> [a] -> m [b]
    , mapM_         -- :: (Monad m) => (a -> m b) -> [a] -> m ()
    , forM          -- :: (Monad m) => [a] -> (a -> m b) -> m [b]
    , forM_         -- :: (Monad m) => [a] -> (a -> m b) -> m ()
    , sequence      -- :: (Monad m) => [m a] -> m [a]
    , sequence_     -- :: (Monad m) => [m a] -> m ()
    , (=<<)         -- :: (Monad m) => (a -> m b) -> m a -> m b
    , (>=>)         -- :: (Monad m) => (a -> m b) -> (b -> m c) -> (a -> m c)
    , (<=<)         -- :: (Monad m) => (b -> m c) -> (a -> m b) -> (a -> m c)
    , forever       -- :: (Monad m) => m a -> m b
    , void

    -- ** Generalisations of list functions

    , join          -- :: (Monad m) => m (m a) -> m a
    , msum          -- :: (MonadPlus m) => [m a] -> m a
    , filterM       -- :: (Monad m) => (a -> m Bool) -> [a] -> m [a]
    , mapAndUnzipM  -- :: (Monad m) => (a -> m (b,c)) -> [a] -> m ([b], [c])
    , zipWithM      -- :: (Monad m) => (a -> b -> m c) -> [a] -> [b] -> m [c]
    , zipWithM_     -- :: (Monad m) => (a -> b -> m c) -> [a] -> [b] -> m ()
    , foldM         -- :: (Monad m) => (a -> b -> m a) -> a -> [b] -> m a 
    , foldM_        -- :: (Monad m) => (a -> b -> m a) -> a -> [b] -> m ()
    , replicateM    -- :: (Monad m) => Int -> m a -> m [a]
    , replicateM_   -- :: (Monad m) => Int -> m a -> m ()

    -- ** Conditional execution of monadic expressions

    , guard         -- :: (MonadPlus m) => Bool -> m ()
    , when          -- :: (Monad m) => Bool -> m () -> m ()
    , unless        -- :: (Monad m) => Bool -> m () -> m ()

    -- ** Monadic lifting operators

    , liftM         -- :: (Monad m) => (a -> b) -> (m a -> m b)
    , liftM2        -- :: (Monad m) => (a -> b -> c) -> (m a -> m b -> m c)
    , liftM3        -- :: ...
    , liftM4        -- :: ...
    , liftM5        -- :: ...

    , ap            -- :: (Monad m) => m (a -> b) -> m a -> m b

  ) where
import "base" Control.Monad

{- $naming

The functions in this library use the following naming conventions: 

* A postfix \'@M@\' always stands for a function in the Kleisli category:
  The monad type constructor @m@ is added to function results
  (modulo currying) and nowhere else.  So, for example, 

>  filter  ::              (a ->   Bool) -> [a] ->   [a]
>  filterM :: (Monad m) => (a -> m Bool) -> [a] -> m [a]

* A postfix \'@_@\' changes the result type from @(m a)@ to @(m ())@.
  Thus, for example: 

>  sequence  :: Monad m => [m a] -> m [a] 
>  sequence_ :: Monad m => [m a] -> m () 

* A prefix \'@m@\' generalizes an existing function to a monadic form.
  Thus, for example: 

>  sum  :: Num a       => [a]   -> a
>  msum :: MonadPlus m => [m a] -> m a

-}