protolude-0.1.10: A sensible set of defaults for writing custom Preludes.

Safe HaskellTrustworthy
LanguageHaskell2010

Monad

Synopsis

Documentation

class Applicative m => Monad m where #

The Monad class defines the basic operations over a monad, a concept from a branch of mathematics known as category theory. From the perspective of a Haskell programmer, however, it is best to think of a monad as an abstract datatype of actions. Haskell's do expressions provide a convenient syntax for writing monadic expressions.

Instances of Monad should satisfy the following laws:

Furthermore, the Monad and Applicative operations should relate as follows:

The above laws imply:

and that pure and (<*>) satisfy the applicative functor laws.

The instances of Monad for lists, Maybe and IO defined in the Prelude satisfy these laws.

Minimal complete definition

(>>=)

Methods

(>>=) :: m a -> (a -> m b) -> m b infixl 1 #

Sequentially compose two actions, passing any value produced by the first as an argument to the second.

(>>) :: m a -> m b -> m b infixl 1 #

Sequentially compose two actions, discarding any value produced by the first, like sequencing operators (such as the semicolon) in imperative languages.

return :: a -> m a #

Inject a value into the monadic type.

Instances

Monad [] 

Methods

(>>=) :: [a] -> (a -> [b]) -> [b] #

(>>) :: [a] -> [b] -> [b] #

return :: a -> [a] #

fail :: String -> [a] #

Monad Maybe 

Methods

(>>=) :: Maybe a -> (a -> Maybe b) -> Maybe b #

(>>) :: Maybe a -> Maybe b -> Maybe b #

return :: a -> Maybe a #

fail :: String -> Maybe a #

Monad IO 

Methods

(>>=) :: IO a -> (a -> IO b) -> IO b #

(>>) :: IO a -> IO b -> IO b #

return :: a -> IO a #

fail :: String -> IO a #

Monad U1 

Methods

(>>=) :: U1 a -> (a -> U1 b) -> U1 b #

(>>) :: U1 a -> U1 b -> U1 b #

return :: a -> U1 a #

fail :: String -> U1 a #

Monad Par1 

Methods

(>>=) :: Par1 a -> (a -> Par1 b) -> Par1 b #

(>>) :: Par1 a -> Par1 b -> Par1 b #

return :: a -> Par1 a #

fail :: String -> Par1 a #

Monad Identity 

Methods

(>>=) :: Identity a -> (a -> Identity b) -> Identity b #

(>>) :: Identity a -> Identity b -> Identity b #

return :: a -> Identity a #

fail :: String -> Identity a #

Monad Min 

Methods

(>>=) :: Min a -> (a -> Min b) -> Min b #

(>>) :: Min a -> Min b -> Min b #

return :: a -> Min a #

fail :: String -> Min a #

Monad Max 

Methods

(>>=) :: Max a -> (a -> Max b) -> Max b #

(>>) :: Max a -> Max b -> Max b #

return :: a -> Max a #

fail :: String -> Max a #

Monad First 

Methods

(>>=) :: First a -> (a -> First b) -> First b #

(>>) :: First a -> First b -> First b #

return :: a -> First a #

fail :: String -> First a #

Monad Last 

Methods

(>>=) :: Last a -> (a -> Last b) -> Last b #

(>>) :: Last a -> Last b -> Last b #

return :: a -> Last a #

fail :: String -> Last a #

Monad Option 

Methods

(>>=) :: Option a -> (a -> Option b) -> Option b #

(>>) :: Option a -> Option b -> Option b #

return :: a -> Option a #

fail :: String -> Option a #

Monad NonEmpty 

Methods

(>>=) :: NonEmpty a -> (a -> NonEmpty b) -> NonEmpty b #

(>>) :: NonEmpty a -> NonEmpty b -> NonEmpty b #

return :: a -> NonEmpty a #

fail :: String -> NonEmpty a #

Monad Complex 

Methods

(>>=) :: Complex a -> (a -> Complex b) -> Complex b #

(>>) :: Complex a -> Complex b -> Complex b #

return :: a -> Complex a #

fail :: String -> Complex a #

Monad STM 

Methods

(>>=) :: STM a -> (a -> STM b) -> STM b #

(>>) :: STM a -> STM b -> STM b #

return :: a -> STM a #

fail :: String -> STM a #

Monad Dual 

Methods

(>>=) :: Dual a -> (a -> Dual b) -> Dual b #

(>>) :: Dual a -> Dual b -> Dual b #

return :: a -> Dual a #

fail :: String -> Dual a #

Monad Sum 

Methods

(>>=) :: Sum a -> (a -> Sum b) -> Sum b #

(>>) :: Sum a -> Sum b -> Sum b #

return :: a -> Sum a #

fail :: String -> Sum a #

Monad Product 

Methods

(>>=) :: Product a -> (a -> Product b) -> Product b #

(>>) :: Product a -> Product b -> Product b #

return :: a -> Product a #

fail :: String -> Product a #

Monad First 

Methods

(>>=) :: First a -> (a -> First b) -> First b #

(>>) :: First a -> First b -> First b #

return :: a -> First a #

fail :: String -> First a #

Monad Last 

Methods

(>>=) :: Last a -> (a -> Last b) -> Last b #

(>>) :: Last a -> Last b -> Last b #

return :: a -> Last a #

fail :: String -> Last a #

Monad Seq 

Methods

(>>=) :: Seq a -> (a -> Seq b) -> Seq b #

(>>) :: Seq a -> Seq b -> Seq b #

return :: a -> Seq a #

fail :: String -> Seq a #

Monad ((->) r) 

Methods

(>>=) :: (r -> a) -> (a -> r -> b) -> r -> b #

(>>) :: (r -> a) -> (r -> b) -> r -> b #

return :: a -> r -> a #

fail :: String -> r -> a #

Monad (Either e) 

Methods

(>>=) :: Either e a -> (a -> Either e b) -> Either e b #

(>>) :: Either e a -> Either e b -> Either e b #

return :: a -> Either e a #

fail :: String -> Either e a #

Monad f => Monad (Rec1 f) 

Methods

(>>=) :: Rec1 f a -> (a -> Rec1 f b) -> Rec1 f b #

(>>) :: Rec1 f a -> Rec1 f b -> Rec1 f b #

return :: a -> Rec1 f a #

fail :: String -> Rec1 f a #

Monoid a => Monad ((,) a) 

Methods

(>>=) :: (a, a) -> (a -> (a, b)) -> (a, b) #

(>>) :: (a, a) -> (a, b) -> (a, b) #

return :: a -> (a, a) #

fail :: String -> (a, a) #

Monad m => Monad (WrappedMonad m) 

Methods

(>>=) :: WrappedMonad m a -> (a -> WrappedMonad m b) -> WrappedMonad m b #

(>>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b #

return :: a -> WrappedMonad m a #

fail :: String -> WrappedMonad m a #

Monad (Proxy *) 

Methods

(>>=) :: Proxy * a -> (a -> Proxy * b) -> Proxy * b #

(>>) :: Proxy * a -> Proxy * b -> Proxy * b #

return :: a -> Proxy * a #

fail :: String -> Proxy * a #

Monad (State s) 

Methods

(>>=) :: State s a -> (a -> State s b) -> State s b #

(>>) :: State s a -> State s b -> State s b #

return :: a -> State s a #

fail :: String -> State s a #

Monad m => Monad (ListT m) 

Methods

(>>=) :: ListT m a -> (a -> ListT m b) -> ListT m b #

(>>) :: ListT m a -> ListT m b -> ListT m b #

return :: a -> ListT m a #

fail :: String -> ListT m a #

Monad m => Monad (MaybeT m) 

Methods

(>>=) :: MaybeT m a -> (a -> MaybeT m b) -> MaybeT m b #

(>>) :: MaybeT m a -> MaybeT m b -> MaybeT m b #

return :: a -> MaybeT m a #

fail :: String -> MaybeT m a #

(Monad f, Monad g) => Monad ((:*:) f g) 

Methods

(>>=) :: (f :*: g) a -> (a -> (f :*: g) b) -> (f :*: g) b #

(>>) :: (f :*: g) a -> (f :*: g) b -> (f :*: g) b #

return :: a -> (f :*: g) a #

fail :: String -> (f :*: g) a #

Monad f => Monad (Alt * f) 

Methods

(>>=) :: Alt * f a -> (a -> Alt * f b) -> Alt * f b #

(>>) :: Alt * f a -> Alt * f b -> Alt * f b #

return :: a -> Alt * f a #

fail :: String -> Alt * f a #

(Monad m, Error e) => Monad (ErrorT e m) 

Methods

(>>=) :: ErrorT e m a -> (a -> ErrorT e m b) -> ErrorT e m b #

(>>) :: ErrorT e m a -> ErrorT e m b -> ErrorT e m b #

return :: a -> ErrorT e m a #

fail :: String -> ErrorT e m a #

Monad m => Monad (ExceptT e m) 

Methods

(>>=) :: ExceptT e m a -> (a -> ExceptT e m b) -> ExceptT e m b #

(>>) :: ExceptT e m a -> ExceptT e m b -> ExceptT e m b #

return :: a -> ExceptT e m a #

fail :: String -> ExceptT e m a #

Monad m => Monad (StateT s m) 

Methods

(>>=) :: StateT s m a -> (a -> StateT s m b) -> StateT s m b #

(>>) :: StateT s m a -> StateT s m b -> StateT s m b #

return :: a -> StateT s m a #

fail :: String -> StateT s m a #

Monad m => Monad (StateT s m) 

Methods

(>>=) :: StateT s m a -> (a -> StateT s m b) -> StateT s m b #

(>>) :: StateT s m a -> StateT s m b -> StateT s m b #

return :: a -> StateT s m a #

fail :: String -> StateT s m a #

(Monoid w, Monad m) => Monad (WriterT w m) 

Methods

(>>=) :: WriterT w m a -> (a -> WriterT w m b) -> WriterT w m b #

(>>) :: WriterT w m a -> WriterT w m b -> WriterT w m b #

return :: a -> WriterT w m a #

fail :: String -> WriterT w m a #

(Monoid w, Monad m) => Monad (WriterT w m) 

Methods

(>>=) :: WriterT w m a -> (a -> WriterT w m b) -> WriterT w m b #

(>>) :: WriterT w m a -> WriterT w m b -> WriterT w m b #

return :: a -> WriterT w m a #

fail :: String -> WriterT w m a #

Monad m => Monad (IdentityT * m) 

Methods

(>>=) :: IdentityT * m a -> (a -> IdentityT * m b) -> IdentityT * m b #

(>>) :: IdentityT * m a -> IdentityT * m b -> IdentityT * m b #

return :: a -> IdentityT * m a #

fail :: String -> IdentityT * m a #

Monad f => Monad (M1 i c f) 

Methods

(>>=) :: M1 i c f a -> (a -> M1 i c f b) -> M1 i c f b #

(>>) :: M1 i c f a -> M1 i c f b -> M1 i c f b #

return :: a -> M1 i c f a #

fail :: String -> M1 i c f a #

Monad m => Monad (ReaderT * r m) 

Methods

(>>=) :: ReaderT * r m a -> (a -> ReaderT * r m b) -> ReaderT * r m b #

(>>) :: ReaderT * r m a -> ReaderT * r m b -> ReaderT * r m b #

return :: a -> ReaderT * r m a #

fail :: String -> ReaderT * r m a #

(Monoid w, Monad m) => Monad (RWST r w s m) 

Methods

(>>=) :: RWST r w s m a -> (a -> RWST r w s m b) -> RWST r w s m b #

(>>) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m b #

return :: a -> RWST r w s m a #

fail :: String -> RWST r w s m a #

(Monoid w, Monad m) => Monad (RWST r w s m) 

Methods

(>>=) :: RWST r w s m a -> (a -> RWST r w s m b) -> RWST r w s m b #

(>>) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m b #

return :: a -> RWST r w s m a #

fail :: String -> RWST r w s m a #

class (Alternative m, Monad m) => MonadPlus m where #

Monads that also support choice and failure.

Methods

mzero :: m a #

the identity of mplus. It should also satisfy the equations

mzero >>= f  =  mzero
v >> mzero   =  mzero

mplus :: m a -> m a -> m a #

an associative operation

Instances

MonadPlus [] 

Methods

mzero :: [a] #

mplus :: [a] -> [a] -> [a] #

MonadPlus Maybe 

Methods

mzero :: Maybe a #

mplus :: Maybe a -> Maybe a -> Maybe a #

MonadPlus IO 

Methods

mzero :: IO a #

mplus :: IO a -> IO a -> IO a #

MonadPlus U1 

Methods

mzero :: U1 a #

mplus :: U1 a -> U1 a -> U1 a #

MonadPlus Option 

Methods

mzero :: Option a #

mplus :: Option a -> Option a -> Option a #

MonadPlus STM 

Methods

mzero :: STM a #

mplus :: STM a -> STM a -> STM a #

MonadPlus Seq 

Methods

mzero :: Seq a #

mplus :: Seq a -> Seq a -> Seq a #

MonadPlus f => MonadPlus (Rec1 f) 

Methods

mzero :: Rec1 f a #

mplus :: Rec1 f a -> Rec1 f a -> Rec1 f a #

MonadPlus (Proxy *) 

Methods

mzero :: Proxy * a #

mplus :: Proxy * a -> Proxy * a -> Proxy * a #

Monad m => MonadPlus (ListT m) 

Methods

mzero :: ListT m a #

mplus :: ListT m a -> ListT m a -> ListT m a #

Monad m => MonadPlus (MaybeT m) 

Methods

mzero :: MaybeT m a #

mplus :: MaybeT m a -> MaybeT m a -> MaybeT m a #

(MonadPlus f, MonadPlus g) => MonadPlus ((:*:) f g) 

Methods

mzero :: (f :*: g) a #

mplus :: (f :*: g) a -> (f :*: g) a -> (f :*: g) a #

MonadPlus f => MonadPlus (Alt * f) 

Methods

mzero :: Alt * f a #

mplus :: Alt * f a -> Alt * f a -> Alt * f a #

(Monad m, Error e) => MonadPlus (ErrorT e m) 

Methods

mzero :: ErrorT e m a #

mplus :: ErrorT e m a -> ErrorT e m a -> ErrorT e m a #

(Monad m, Monoid e) => MonadPlus (ExceptT e m) 

Methods

mzero :: ExceptT e m a #

mplus :: ExceptT e m a -> ExceptT e m a -> ExceptT e m a #

MonadPlus m => MonadPlus (StateT s m) 

Methods

mzero :: StateT s m a #

mplus :: StateT s m a -> StateT s m a -> StateT s m a #

MonadPlus m => MonadPlus (StateT s m) 

Methods

mzero :: StateT s m a #

mplus :: StateT s m a -> StateT s m a -> StateT s m a #

(Monoid w, MonadPlus m) => MonadPlus (WriterT w m) 

Methods

mzero :: WriterT w m a #

mplus :: WriterT w m a -> WriterT w m a -> WriterT w m a #

(Monoid w, MonadPlus m) => MonadPlus (WriterT w m) 

Methods

mzero :: WriterT w m a #

mplus :: WriterT w m a -> WriterT w m a -> WriterT w m a #

MonadPlus m => MonadPlus (IdentityT * m) 

Methods

mzero :: IdentityT * m a #

mplus :: IdentityT * m a -> IdentityT * m a -> IdentityT * m a #

MonadPlus f => MonadPlus (M1 i c f) 

Methods

mzero :: M1 i c f a #

mplus :: M1 i c f a -> M1 i c f a -> M1 i c f a #

MonadPlus m => MonadPlus (ReaderT * r m) 

Methods

mzero :: ReaderT * r m a #

mplus :: ReaderT * r m a -> ReaderT * r m a -> ReaderT * r m a #

(Monoid w, MonadPlus m) => MonadPlus (RWST r w s m) 

Methods

mzero :: RWST r w s m a #

mplus :: RWST r w s m a -> RWST r w s m a -> RWST r w s m a #

(Monoid w, MonadPlus m) => MonadPlus (RWST r w s m) 

Methods

mzero :: RWST r w s m a #

mplus :: RWST r w s m a -> RWST r w s m a -> RWST r w s m a #

(=<<) :: Monad m => (a -> m b) -> m a -> m b infixr 1 #

Same as >>=, but with the arguments interchanged.

(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c infixr 1 #

Left-to-right Kleisli composition of monads.

(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c infixr 1 #

Right-to-left Kleisli composition of monads. (>=>), with the arguments flipped.

Note how this operator resembles function composition (.):

(.)   ::            (b ->   c) -> (a ->   b) -> a ->   c
(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c

(>>) :: Monad m => forall a b. m a -> m b -> m b #

Sequentially compose two actions, discarding any value produced by the first, like sequencing operators (such as the semicolon) in imperative languages.

forever :: Applicative f => f a -> f b #

forever act repeats the action infinitely.

join :: Monad m => m (m a) -> m a #

The join function is the conventional monad join operator. It is used to remove one level of monadic structure, projecting its bound argument into the outer level.

mfilter :: MonadPlus m => (a -> Bool) -> m a -> m a #

Direct MonadPlus equivalent of filter filter = (mfilter:: (a -> Bool) -> [a] -> [a] applicable to any MonadPlus, for example mfilter odd (Just 1) == Just 1 mfilter odd (Just 2) == Nothing

filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a] #

This generalizes the list-based filter function.

mapAndUnzipM :: Applicative m => (a -> m (b, c)) -> [a] -> m ([b], [c]) #

The mapAndUnzipM function maps its first argument over a list, returning the result as a pair of lists. This function is mainly used with complicated data structures or a state-transforming monad.

zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c] #

The zipWithM function generalizes zipWith to arbitrary applicative functors.

zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m () #

zipWithM_ is the extension of zipWithM which ignores the final result.

foldM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b #

The foldM function is analogous to foldl, except that its result is encapsulated in a monad. Note that foldM works from left-to-right over the list arguments. This could be an issue where (>>) and the `folded function' are not commutative.

      foldM f a1 [x1, x2, ..., xm]

==

      do
        a2 <- f a1 x1
        a3 <- f a2 x2
        ...
        f am xm

If right-to-left evaluation is required, the input list should be reversed.

Note: foldM is the same as foldlM

foldM_ :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m () #

Like foldM, but discards the result.

replicateM :: Applicative m => Int -> m a -> m [a] #

replicateM n act performs the action n times, gathering the results.

replicateM_ :: Applicative m => Int -> m a -> m () #

Like replicateM, but discards the result.

concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b] Source #

guard :: Alternative f => Bool -> f () #

guard b is pure () if b is True, and empty if b is False.

when :: Applicative f => Bool -> f () -> f () #

Conditional execution of Applicative expressions. For example,

when debug (putStrLn "Debugging")

will output the string Debugging if the Boolean value debug is True, and otherwise do nothing.

unless :: Applicative f => Bool -> f () -> f () #

The reverse of when.

liftM :: Monad m => (a1 -> r) -> m a1 -> m r #

Promote a function to a monad.

liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r #

Promote a function to a monad, scanning the monadic arguments from left to right. For example,

   liftM2 (+) [0,1] [0,2] = [0,2,1,3]
   liftM2 (+) (Just 1) Nothing = Nothing

liftM3 :: Monad m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r #

Promote a function to a monad, scanning the monadic arguments from left to right (cf. liftM2).

liftM4 :: Monad m => (a1 -> a2 -> a3 -> a4 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m r #

Promote a function to a monad, scanning the monadic arguments from left to right (cf. liftM2).

liftM5 :: Monad m => (a1 -> a2 -> a3 -> a4 -> a5 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> m r #

Promote a function to a monad, scanning the monadic arguments from left to right (cf. liftM2).

liftM' :: Monad m => (a -> b) -> m a -> m b Source #

liftM2' :: Monad m => (a -> b -> c) -> m a -> m b -> m c Source #

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

In many situations, the liftM operations can be replaced by uses of ap, which promotes function application.

      return f `ap` x1 `ap` ... `ap` xn

is equivalent to

      liftMn f x1 x2 ... xn

(<$!>) :: Monad m => (a -> b) -> m a -> m b Source #