Modulererebase-1.21.2Haskell2010

Control.Monad.Trans.Cont

2 types
14 values

Packagererebase-1.21.2
Exports16
LanguageHaskell2010
LicenceMIT
SourceCont.hs

typetype 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.

valuecont :: ((a -> r) -> r) -> Cont r a

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

valueevalCont :: Cont r r -> r

The result of running a CPS computation with the identity as the final continuation.

```
evalCont (return x) = x
```

valueevalContT :: Monad m => ContT r m r -> m r

The result of running a CPS computation with return as the final continuation.

```
evalContT (lift m) = m
```

valueliftLocal

:: Monad m
=> m r'
-> (r' -> r') -> m r -> m r
-> r' -> r'
-> ContT r m a
-> ContT r m a

liftLocal ask local yields a local function for ContT r m.

valuemapCont :: (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
```

valuemapContT :: (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

valuereset :: Cont r r -> Cont r' r

reset m delimits the continuation of any shift inside m.

```
reset (return m) = return m
```

valueresetT :: Monad m => ContT r m r -> ContT r' m r

resetT m delimits the continuation of any shiftT inside m.

```
resetT (lift m) = lift m
```

valuerunCont

:: 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)

valueshiftT :: Monad m => ((a -> m r) -> ContT r m r) -> ContT r m a

shiftT f captures the continuation up to the nearest enclosing resetT and passes it to f:

resetT (shiftT f >>= k) = resetT (f (evalContT . k))

valuewithCont :: ((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
```

valuewithContT :: ((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

valueshift :: ((a -> r) -> Cont r r) -> Cont r a

shift f captures the continuation up to the nearest enclosing reset and passes it to f:

reset (shift f >>= k) = reset (f (evalCont . k))

valuecallCC :: ((a -> ContT r m b) -> ContT r m a) -> ContT r m a

callCC (call-with-current-continuation) calls its argument function, passing it the current continuation. It provides an escape continuation mechanism for use with continuation monads. Escape continuations one allow to abort the current computation and return a value immediately. They achieve a similar effect to throwE and catchE within an ExceptT monad. The advantage of this function over calling return is that it makes the continuation explicit, allowing more flexibility and better control.

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.

newtypenewtype ContT (r :: k) (m :: k -> Type) a

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

Instances24MonadAccum, MonadReader, MonadState, MonadSelect, MonadBase, MonadFree, …

MonadAccum w m => MonadAccum w (ContT r m)Defined in mtl-2.3.1 · Control.Monad.Accum
The continuation can see, and interact with, the accumulated value.
MonadReader r' m => MonadReader r' (ContT r m)Defined in mtl-2.3.1 · Control.Monad.Reader.Class
MonadState s m => MonadState s (ContT r m)Defined in mtl-2.3.1 · Control.Monad.State.Class
MonadSelect r' m => MonadSelect r' (ContT r m)Defined in mtl-2.3.1 · Control.Monad.Select
The continuation describes a way of choosing a 'search' or 'ranking' strategy for r, based on a 'ranking' using r', given any a. We then get a 'search' strategy for r.
MonadBase b m => MonadBase b (ContT r m)Defined in transformers-base-0.4.6 · Control.Monad.Base
(Functor f, MonadFree f m) => MonadFree f (ContT r m)Defined in free-5.2 · Control.Monad.Free.Class
MonadTrans (ContT r)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Cont
BindTrans (ContT r)Defined in semigroupoids-6.0.1 · Data.Functor.Bind.Trans
Monad (ContT r m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Cont
Functor (ContT r m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Cont
MonadFail m => MonadFail (ContT r m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Cont
Applicative (ContT r m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Cont
MonadIO m => MonadIO (ContT r m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Cont
MonadCont (ContT r m)Defined in mtl-2.3.1 · Control.Monad.Cont.Class
MonadThrow m => MonadThrow (ContT r m)Defined in exceptions-0.10.9 · Control.Monad.Catch
PrimMonad m => PrimMonad (ContT r m)Defined in primitive-0.9.1.0 · Control.Monad.Primitive
Apply (ContT r m)Defined in semigroupoids-6.0.1 · Data.Functor.Bind.Class
Bind (ContT r m)Defined in semigroupoids-6.0.1 · Data.Functor.Bind.Class
Invariant (ContT r m)Defined in invariant-0.6.4 · Data.Functor.Invariant
from the transformers package
Selective (ContT r m)Defined in selective-0.7.0.1 · Control.Selective
Pointed (ContT r m)Defined in pointed-5.0.4 · Data.Pointed
Generic (ContT r m a)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Cont
type Rep (ContT r m a) = D1 ('MetaData "ContT" "Control.Monad.Trans.Cont" "transformers-0.6.1.1-a11a" 'True) (C1 ('MetaCons "ContT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runContT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 ((a -> m r) -> m r))))Defined in transformers-0.6.1.1 · Control.Monad.Trans.Cont
type PrimState (ContT r m) = PrimState mDefined in primitive-0.9.1.0 · Control.Monad.Primitive