Prologue.Control.Monad.Primitive

Documentation

data RealWorld :: Type

RealWorld is deeply magical. It is primitive, but it is not unlifted (hence ptrArg). We never manipulate values of type RealWorld; it's only used in the type system, to parameterise State#.

data IO a

A value of type IO a is a computation which, when performed, does some I/O before returning a value of type a.

There is really only one way to "perform" an I/O action: bind it to Main.main in your program. When your program is run, the I/O will be performed. It isn't possible to perform I/O from an arbitrary function, unless that function is itself in the IO monad and called at some point, directly or indirectly, from Main.main.

IO is a monad, so IO actions can be combined using either the do-notation or the >> and >>= operations from the Monad class.

Instances

Monad IO

Since: base-2.1

Defined in GHC.Base

Methods

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

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

return :: a -> IO a

fail :: String -> IO a

Functor IO

Since: base-2.1

Defined in GHC.Base

Methods

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

(<$) :: a -> IO b -> IO a

MonadFix IO

Since: base-2.1

Defined in Control.Monad.Fix

Methods

mfix :: (a -> IO a) -> IO a

MonadFail IO

Since: base-4.9.0.0

Defined in Control.Monad.Fail

Methods

fail :: String -> IO a

Applicative IO

Since: base-2.1

Defined in GHC.Base

Methods

pure :: a -> IO a

(<*>) :: IO (a -> b) -> IO a -> IO b

liftA2 :: (a -> b -> c) -> IO a -> IO b -> IO c

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

(<*) :: IO a -> IO b -> IO a

Alternative IO

Since: base-4.9.0.0

Defined in GHC.Base

Methods

empty :: IO a

(<|>) :: IO a -> IO a -> IO a

some :: IO a -> IO [a]

many :: IO a -> IO [a]

MonadPlus IO

Since: base-4.9.0.0

Defined in GHC.Base

Methods

mzero :: IO a

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

MonadIO IO

Since: base-4.9.0.0

Defined in Control.Monad.IO.Class

Methods

liftIO :: IO a -> IO a

MonadThrow IO

Defined in Control.Monad.Catch

Methods

throwM :: Exception e => e -> IO a

MonadCatch IO

Defined in Control.Monad.Catch

Methods

catch :: Exception e => IO a -> (e -> IO a) -> IO a

MonadMask IO

Defined in Control.Monad.Catch

Methods

mask :: ((forall a. IO a -> IO a) -> IO b) -> IO b

uninterruptibleMask :: ((forall a. IO a -> IO a) -> IO b) -> IO b

generalBracket :: IO a -> (a -> ExitCase b -> IO c) -> (a -> IO b) -> IO (b, c)

Apply IO

Defined in Data.Functor.Bind.Class

Methods

(<.>) :: IO (a -> b) -> IO a -> IO b

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

(<.) :: IO a -> IO b -> IO a

liftF2 :: (a -> b -> c) -> IO a -> IO b -> IO c

Pointed IO

Defined in Data.Pointed

Methods

point :: a -> IO a

PrimMonad IO

Defined in Control.Monad.Primitive

Associated Types

type PrimState IO :: Type

Methods

primitive :: (State# (PrimState IO) -> (#State# (PrimState IO), a#)) -> IO a

PrimBase IO

Defined in Control.Monad.Primitive

Methods

internal :: IO a -> State# (PrimState IO) -> (#State# (PrimState IO), a#)

Alt IO

This instance does not actually satisfy the (<.>) right distributive law It instead satisfies the "Left-Catch" law

Defined in Data.Functor.Alt

Methods

(<!>) :: IO a -> IO a -> IO a

some :: Applicative IO => IO a -> IO [a]

many :: Applicative IO => IO a -> IO [a]

Bind IO

Defined in Data.Functor.Bind.Class

Methods

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

join :: IO (IO a) -> IO a

Quasi IO

Defined in Language.Haskell.TH.Syntax

Methods

qNewName :: String -> IO Name

qReport :: Bool -> String -> IO ()

qRecover :: IO a -> IO a -> IO a

qLookupName :: Bool -> String -> IO (Maybe Name)

qReify :: Name -> IO Info

qReifyFixity :: Name -> IO (Maybe Fixity)

qReifyInstances :: Name -> [Type] -> IO [Dec]

qReifyRoles :: Name -> IO [Role]

qReifyAnnotations :: Data a => AnnLookup -> IO [a]

qReifyModule :: Module -> IO ModuleInfo

qReifyConStrictness :: Name -> IO [DecidedStrictness]

qLocation :: IO Loc

qRunIO :: IO a -> IO a

qAddDependentFile :: FilePath -> IO ()

qAddTempFile :: String -> IO FilePath

qAddTopDecls :: [Dec] -> IO ()

qAddForeignFilePath :: ForeignSrcLang -> String -> IO ()

qAddModFinalizer :: Q () -> IO ()

qAddCorePlugin :: String -> IO ()

qGetQ :: Typeable a => IO (Maybe a)

qPutQ :: Typeable a => a -> IO ()

qIsExtEnabled :: Extension -> IO Bool

qExtsEnabled :: IO [Extension]

Semigroup a => Semigroup (IO a)

Since: base-4.10.0.0

Defined in GHC.Base

Methods

(<>) :: IO a -> IO a -> IO a

sconcat :: NonEmpty (IO a) -> IO a

stimes :: Integral b => b -> IO a -> IO a

Monoid a => Monoid (IO a)

Since: base-4.9.0.0

Defined in GHC.Base

Methods

mempty :: IO a

mappend :: IO a -> IO a -> IO a

mconcat :: [IO a] -> IO a

Default a => Default (IO a)

Defined in Data.Default.Class

Methods

def :: IO a

type PrimState IO

Defined in Control.Monad.Primitive

type PrimState IO = RealWorld

class Monad m => MonadIO (m :: Type -> Type) where

Monads in which IO computations may be embedded. Any monad built by applying a sequence of monad transformers to the IO monad will be an instance of this class.

Instances should satisfy the following laws, which state that liftIO is a transformer of monads:

• liftIO . return = return

• liftIO (m >>= f) = liftIO m >>= (liftIO . f)

Methods

liftIO :: IO a -> m a

Lift a computation from the IO monad.

Instances

MonadIO IO

Since: base-4.9.0.0

Defined in Control.Monad.IO.Class

Methods

liftIO :: IO a -> IO a

MonadIO Q

Defined in Language.Haskell.TH.Syntax

Methods

liftIO :: IO a -> Q a

MonadIO m => MonadIO (MaybeT m)

Defined in Control.Monad.Trans.Maybe

Methods

liftIO :: IO a -> MaybeT m a

MonadIO m => MonadIO (IdentityT m)

Defined in Control.Monad.Trans.Identity

Methods

liftIO :: IO a -> IdentityT m a

MonadIO m => MonadIO (ExceptT e m)

Defined in Control.Monad.Trans.Except

Methods

liftIO :: IO a -> ExceptT e m a

(Functor f, MonadIO m) => MonadIO (FreeT f m)

Defined in Control.Monad.Trans.Free

Methods

liftIO :: IO a -> FreeT f m a

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

Defined in Control.Monad.Trans.Error

Methods

liftIO :: IO a -> ErrorT e m a

liftPrim :: (PrimBase m1, PrimMonad m2, PrimState m1 ~ PrimState m2) => m1 a -> m2 a

Lifts a PrimBase into another PrimMonad with the same underlying state token type.

primitive_ :: PrimMonad m => (State# (PrimState m) -> State# (PrimState m)) -> m ()

Execute a primitive operation with no result

class Monad m => PrimMonad (m :: Type -> Type) where

Class of monads which can perform primitive state-transformer actions

Associated Types

type PrimState (m :: Type -> Type) :: Type

State token type

Methods

primitive :: (State# (PrimState m) -> (#State# (PrimState m), a#)) -> m a

Execute a primitive operation

Instances

PrimMonad IO

Defined in Control.Monad.Primitive

Associated Types

type PrimState IO :: Type

Methods

primitive :: (State# (PrimState IO) -> (#State# (PrimState IO), a#)) -> IO a

PrimMonad (ST s)

Defined in Control.Monad.Primitive

Associated Types

type PrimState (ST s) :: Type

Methods

primitive :: (State# (PrimState (ST s)) -> (#State# (PrimState (ST s)), a#)) -> ST s a

PrimMonad m => PrimMonad (MaybeT m)

Defined in Control.Monad.Primitive

Associated Types

type PrimState (MaybeT m) :: Type

Methods

primitive :: (State# (PrimState (MaybeT m)) -> (#State# (PrimState (MaybeT m)), a#)) -> MaybeT m a

PrimMonad m => PrimMonad (ListT m)

Defined in Control.Monad.Primitive

Associated Types

type PrimState (ListT m) :: Type

Methods

primitive :: (State# (PrimState (ListT m)) -> (#State# (PrimState (ListT m)), a#)) -> ListT m a

PrimMonad m => PrimMonad (IdentityT m)

Defined in Control.Monad.Primitive

Associated Types

type PrimState (IdentityT m) :: Type

Methods

primitive :: (State# (PrimState (IdentityT m)) -> (#State# (PrimState (IdentityT m)), a#)) -> IdentityT m a

PrimMonad m => PrimMonad (ExceptT e m)

Defined in Control.Monad.Primitive

Associated Types

type PrimState (ExceptT e m) :: Type

Methods

primitive :: (State# (PrimState (ExceptT e m)) -> (#State# (PrimState (ExceptT e m)), a#)) -> ExceptT e m a

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

Defined in Control.Monad.Primitive

Associated Types

type PrimState (ErrorT e m) :: Type

Methods

primitive :: (State# (PrimState (ErrorT e m)) -> (#State# (PrimState (ErrorT e m)), a#)) -> ErrorT e m a

PrimMonad m => PrimMonad (StateT s m)

Defined in Control.Monad.Primitive

Associated Types

type PrimState (StateT s m) :: Type

Methods

primitive :: (State# (PrimState (StateT s m)) -> (#State# (PrimState (StateT s m)), a#)) -> StateT s m a

PrimMonad m => PrimMonad (StateT s m)

Defined in Control.Monad.Primitive

Associated Types

type PrimState (StateT s m) :: Type

Methods

primitive :: (State# (PrimState (StateT s m)) -> (#State# (PrimState (StateT s m)), a#)) -> StateT s m a

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

Defined in Control.Monad.Primitive

Associated Types

type PrimState (WriterT w m) :: Type

Methods

primitive :: (State# (PrimState (WriterT w m)) -> (#State# (PrimState (WriterT w m)), a#)) -> WriterT w m a

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

Defined in Control.Monad.Primitive

Associated Types

type PrimState (WriterT w m) :: Type

Methods

primitive :: (State# (PrimState (WriterT w m)) -> (#State# (PrimState (WriterT w m)), a#)) -> WriterT w m a

(Monoid w, PrimMonad m) => PrimMonad (AccumT w m)

Since: primitive-0.6.3.0

Defined in Control.Monad.Primitive

Associated Types

type PrimState (AccumT w m) :: Type

Methods

primitive :: (State# (PrimState (AccumT w m)) -> (#State# (PrimState (AccumT w m)), a#)) -> AccumT w m a

PrimMonad m => PrimMonad (SelectT r m)

Defined in Control.Monad.Primitive

Associated Types

type PrimState (SelectT r m) :: Type

Methods

primitive :: (State# (PrimState (SelectT r m)) -> (#State# (PrimState (SelectT r m)), a#)) -> SelectT r m a

PrimMonad m => PrimMonad (ContT r m)

Since: primitive-0.6.3.0

Defined in Control.Monad.Primitive

Associated Types

type PrimState (ContT r m) :: Type

Methods

primitive :: (State# (PrimState (ContT r m)) -> (#State# (PrimState (ContT r m)), a#)) -> ContT r m a

PrimMonad m => PrimMonad (ReaderT r m)

Defined in Control.Monad.Primitive

Associated Types

type PrimState (ReaderT r m) :: Type

Methods

primitive :: (State# (PrimState (ReaderT r m)) -> (#State# (PrimState (ReaderT r m)), a#)) -> ReaderT r m a

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

Defined in Control.Monad.Primitive

Associated Types

type PrimState (RWST r w s m) :: Type

Methods

primitive :: (State# (PrimState (RWST r w s m)) -> (#State# (PrimState (RWST r w s m)), a#)) -> RWST r w s m a

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

Defined in Control.Monad.Primitive

Associated Types

type PrimState (RWST r w s m) :: Type

Methods

primitive :: (State# (PrimState (RWST r w s m)) -> (#State# (PrimState (RWST r w s m)), a#)) -> RWST r w s m a

class PrimMonad m => PrimBase (m :: Type -> Type)

Class of primitive monads for state-transformer actions.

Unlike PrimMonad, this typeclass requires that the Monad be fully expressed as a state transformer, therefore disallowing other monad transformers on top of the base IO or ST.

Since: primitive-0.6.0.0

Minimal complete definition

internal

Instances

PrimBase IO

Defined in Control.Monad.Primitive

Methods

internal :: IO a -> State# (PrimState IO) -> (#State# (PrimState IO), a#)

PrimBase (ST s)

Defined in Control.Monad.Primitive

Methods

internal :: ST s a -> State# (PrimState (ST s)) -> (#State# (PrimState (ST s)), a#)

PrimBase m => PrimBase (IdentityT m)

Since: primitive-0.6.2.0

Defined in Control.Monad.Primitive

Methods

internal :: IdentityT m a -> State# (PrimState (IdentityT m)) -> (#State# (PrimState (IdentityT m)), a#)