Safe Haskell	Safe
Language	Haskell2010

Cont

Contents

Cont
ContT
MonadCont

Synopsis

type Cont r = ContT r Identity
cont :: ((a -> r) -> r) -> Cont r a
runCont :: Cont r a -> (a -> r) -> r
mapCont :: (r -> r) -> Cont r a -> Cont r a
withCont :: ((b -> r) -> a -> r) -> Cont r a -> Cont r b
newtype ContT (r :: k) (m :: k -> *) a :: forall k. k -> (k -> *) -> * -> * = ContT {
- runContT :: (a -> m r) -> m r
}
mapContT :: (m r -> m r) -> ContT r m a -> ContT r m a
withContT :: ((b -> m r) -> a -> m r) -> ContT r m a -> ContT r m b
class Monad m => MonadCont (m :: * -> *) where

Cont

type Cont r = ContT r Identity #

Continuation monad. Cont r a is a CPS ("continuation-passing style") computation that produces an intermediate result of type a within a CPS computation whose final result type is r.

The return function simply creates a continuation which passes the value on.

The >>= operator adds the bound function into the continuation chain.

cont :: ((a -> r) -> r) -> Cont r a #

Construct a continuation-passing computation from a function. (The inverse of runCont)

runCont #

Arguments

:: Cont r a	continuation computation (`Cont`).
-> (a -> r)	the final continuation, which produces the final result (often `id`).
-> r

The result of running a CPS computation with a given final continuation. (The inverse of cont)

mapCont :: (r -> r) -> Cont r a -> Cont r a #

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

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

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

Apply a function to transform the continuation passed to a CPS computation.

```
runCont (withCont f m) = runCont m . f
```

ContT

newtype ContT (r :: k) (m :: k -> *) a :: forall k. k -> (k -> *) -> * -> * #

The continuation monad transformer. Can be used to add continuation handling to any type constructor: the Monad instance and most of the operations do not require m to be a monad.

ContT is not a functor on the category of monads, and many operations cannot be lifted through it.

Constructors

ContT
Fields runContT :: (a -> m r) -> m r

Instances

MonadReader r' m => MonadReader r' (ContT r m)
Instance details Defined in Control.Monad.Reader.Class Methods ask :: ContT r m r' # local :: (r' -> r') -> ContT r m a -> ContT r m a # reader :: (r' -> a) -> ContT r m a #
MonadState s m => MonadState s (ContT r m)
Instance details Defined in Control.Monad.State.Class Methods get :: ContT r m s # put :: s -> ContT r m () # state :: (s -> (a, s)) -> ContT r m a #
(Functor f, MonadFree f m) => MonadFree f (ContT r m)
Instance details Defined in Control.Monad.Free.Class Methods wrap :: f (ContT r m a) -> ContT r m a #
MonadBase b m => MonadBase b (ContT r m)
Instance details Defined in Control.Monad.Base Methods liftBase :: b α -> ContT r m α #
MonadTrans (ContT r)
Instance details Defined in Control.Monad.Trans.Cont Methods lift :: Monad m => m a -> ContT r m a #
Monad (ContT r m)
Instance details Defined in Control.Monad.Trans.Cont Methods (>>=) :: ContT r m a -> (a -> ContT r m b) -> ContT r m b # (>>) :: ContT r m a -> ContT r m b -> ContT r m b # return :: a -> ContT r m a # fail :: String -> ContT r m a #
Functor (ContT r m)
Instance details Defined in Control.Monad.Trans.Cont Methods fmap :: (a -> b) -> ContT r m a -> ContT r m b # (<$) :: a -> ContT r m b -> ContT r m a #
MonadFail m => MonadFail (ContT r m)
Instance details Defined in Control.Monad.Trans.Cont Methods fail :: String -> ContT r m a #
Applicative (ContT r m)
Instance details Defined in Control.Monad.Trans.Cont Methods pure :: a -> ContT r m a # (<>) :: ContT r m (a -> b) -> ContT r m a -> ContT r m b # liftA2 :: (a -> b -> c) -> ContT r m a -> ContT r m b -> ContT r m c # (>) :: ContT r m a -> ContT r m b -> ContT r m b # (<*) :: ContT r m a -> ContT r m b -> ContT r m a #
MonadIO m => MonadIO (ContT r m)
Instance details Defined in Control.Monad.Trans.Cont Methods liftIO :: IO a -> ContT r m a #
MonadThrow m => MonadThrow (ContT r m)
Instance details Defined in Control.Monad.Catch Methods throwM :: Exception e => e -> ContT r m a #
PrimMonad m => PrimMonad (ContT r m)	Since: primitive-0.6.3.0
Instance details Defined in Control.Monad.Primitive Associated Types type PrimState (ContT r m) :: * # Methods primitive :: (State# (PrimState (ContT r m)) -> (#State# (PrimState (ContT r m)), a#)) -> ContT r m a #
Apply (ContT r m)
Instance details Defined in Data.Functor.Bind.Class Methods (<.>) :: ContT r m (a -> b) -> ContT r m a -> ContT r m b # (.>) :: ContT r m a -> ContT r m b -> ContT r m b # (<.) :: ContT r m a -> ContT r m b -> ContT r m a # liftF2 :: (a -> b -> c) -> ContT r m a -> ContT r m b -> ContT r m c #
MonadManaged m => MonadManaged (ContT r m)
Instance details Defined in Control.Monad.Managed Methods using :: Managed a -> ContT r m a #
MonadCont (ContT r m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> ContT r m b) -> ContT r m a) -> ContT r m a #
Pointed (ContT r m)
Instance details Defined in Data.Pointed Methods point :: a -> ContT r m a #
Bind (ContT r m)
Instance details Defined in Data.Functor.Bind.Class Methods (>>-) :: ContT r m a -> (a -> ContT r m b) -> ContT r m b # join :: ContT r m (ContT r m a) -> ContT r m a #
Wrapped (ContT r m a)
Instance details Defined in Control.Lens.Wrapped Associated Types type Unwrapped (ContT r m a) :: * # Methods _Wrapped' :: Iso' (ContT r m a) (Unwrapped (ContT r m a)) #
t ~ ContT r' m' a' => Rewrapped (ContT r m a) t
Instance details Defined in Control.Lens.Wrapped
type PrimState (ContT r m)
Instance details Defined in Control.Monad.Primitive type PrimState (ContT r m) = PrimState m
type Unwrapped (ContT r m a)
Instance details Defined in Control.Lens.Wrapped type Unwrapped (ContT r m a) = (a -> m r) -> m r

mapContT :: (m r -> m r) -> ContT r m a -> ContT r m a #

Apply a function to transform the result of a continuation-passing computation. This has a more restricted type than the map operations for other monad transformers, because ContT does not define a functor in the category of monads.

runContT (mapContT f m) = f . runContT m

withContT :: ((b -> m r) -> a -> m r) -> ContT r m a -> ContT r m b #

Apply a function to transform the continuation passed to a CPS computation.

runContT (withContT f m) = runContT m . f

MonadCont

class Monad m => MonadCont (m :: * -> *) where #

Minimal complete definition

callCC

Methods

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

callCC (call-with-current-continuation) calls a function with the current continuation as its argument. Provides an escape continuation mechanism for use with Continuation monads. Escape continuations allow to abort the current computation and return a value immediately. They achieve a similar effect to throwError and catchError within an Error monad. Advantage of this function over calling return is that it makes the continuation explicit, allowing more flexibility and better control (see examples in Control.Monad.Cont).

The standard idiom used with callCC is to provide a lambda-expression to name the continuation. Then calling the named continuation anywhere within its scope will escape from the computation, even if it is many layers deep within nested computations.

Instances

MonadCont m => MonadCont (MaybeT m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> MaybeT m b) -> MaybeT m a) -> MaybeT m a #
(Functor m, MonadCont m) => MonadCont (Free m)
Instance details Defined in Control.Monad.Free Methods callCC :: ((a -> Free m b) -> Free m a) -> Free m a #
MonadCont m => MonadCont (ListT m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> ListT m b) -> ListT m a) -> ListT m a #
MonadCont m => MonadCont (IdentityT m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> IdentityT m b) -> IdentityT m a) -> IdentityT m a #
MonadCont m => MonadCont (ExceptT e m)	Since: mtl-2.2
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> ExceptT e m b) -> ExceptT e m a) -> ExceptT e m a #
(Functor f, MonadCont m) => MonadCont (FreeT f m)
Instance details Defined in Control.Monad.Trans.Free Methods callCC :: ((a -> FreeT f m b) -> FreeT f m a) -> FreeT f m a #
(Error e, MonadCont m) => MonadCont (ErrorT e m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> ErrorT e m b) -> ErrorT e m a) -> ErrorT e m a #
(Monoid w, MonadCont m) => MonadCont (WriterT w m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> WriterT w m b) -> WriterT w m a) -> WriterT w m a #
MonadCont m => MonadCont (StateT s m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> StateT s m b) -> StateT s m a) -> StateT s m a #
MonadCont m => MonadCont (StateT s m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> StateT s m b) -> StateT s m a) -> StateT s m a #
(Monoid w, MonadCont m) => MonadCont (WriterT w m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> WriterT w m b) -> WriterT w m a) -> WriterT w m a #
MonadCont m => MonadCont (ReaderT r m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> ReaderT r m b) -> ReaderT r m a) -> ReaderT r m a #
(Stream s, MonadCont m) => MonadCont (ParsecT e s m)
Instance details Defined in Text.Megaparsec.Internal Methods callCC :: ((a -> ParsecT e s m b) -> ParsecT e s m a) -> ParsecT e s m a #
MonadCont (ContT r m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> ContT r m b) -> ContT r m a) -> ContT r m a #
(Monoid w, MonadCont m) => MonadCont (RWST r w s m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> RWST r w s m b) -> RWST r w s m a) -> RWST r w s m a #
(Monoid w, MonadCont m) => MonadCont (RWST r w s m)
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> RWST r w s m b) -> RWST r w s m a) -> RWST r w s m a #