Control.Carrier.State.Lazy

A carrier for the State effect that refrains from evaluating its state until necessary. This is less efficient than Control.Carrier.State.Strict but allows some cyclic computations to terminate that would loop infinitely in a strict state carrier.

Note that the parameter order in runState, evalState, and execState is reversed compared the equivalent functions provided by transformers. This is an intentional decision made to enable the composition of effect handlers with . without invoking flip.

Since: 1.0.0.0

Lazy state carrier

runState :: s -> StateC s m a -> m (s, a)

Run a lazy State effect, yielding the result value and the final state. More programs terminate with lazy state than strict state, but injudicious use of lazy state may lead to thunk buildup.

runState s (pure a) = pure (s, a)

runState s get = pure (s, s)

runState s (put t) = pure (t, ())

Since: 1.0.0.0

evalState :: forall s m a. Functor m => s -> StateC s m a -> m a

Run a lazy State effect, yielding the result value and discarding the final state.

evalState s m = fmap snd (runState s m)

Since: 1.0.0.0

execState :: forall s m a. Functor m => s -> StateC s m a -> m s

Run a lazy State effect, yielding the final state and discarding the return value.

execState s m = fmap fst (runState s m)

Since: 1.0.0.0

newtype StateC s m a

Since: 1.0.0.0

Constructors

StateC (s -> m (s, a))

Instances

MonadTrans (StateC s)

Defined in Control.Carrier.State.Lazy

Methods

lift :: Monad m => m a -> StateC s m a

Monad m => Monad (StateC s m)

Defined in Control.Carrier.State.Lazy

Methods

(>>=) :: StateC s m a -> (a -> StateC s m b) -> StateC s m b

(>>) :: StateC s m a -> StateC s m b -> StateC s m b

return :: a -> StateC s m a

fail :: String -> StateC s m a

Functor m => Functor (StateC s m)

Defined in Control.Carrier.State.Lazy

Methods

fmap :: (a -> b) -> StateC s m a -> StateC s m b

(<$) :: a -> StateC s m b -> StateC s m a

MonadFix m => MonadFix (StateC s m)

Defined in Control.Carrier.State.Lazy

Methods

mfix :: (a -> StateC s m a) -> StateC s m a

MonadFail m => MonadFail (StateC s m)

Defined in Control.Carrier.State.Lazy

Methods

fail :: String -> StateC s m a

Monad m => Applicative (StateC s m)

Defined in Control.Carrier.State.Lazy

Methods

pure :: a -> StateC s m a

(<*>) :: StateC s m (a -> b) -> StateC s m a -> StateC s m b

liftA2 :: (a -> b -> c) -> StateC s m a -> StateC s m b -> StateC s m c

(*>) :: StateC s m a -> StateC s m b -> StateC s m b

(<*) :: StateC s m a -> StateC s m b -> StateC s m a

MonadIO m => MonadIO (StateC s m)

Defined in Control.Carrier.State.Lazy

Methods

liftIO :: IO a -> StateC s m a

(Alternative m, Monad m) => Alternative (StateC s m)

Defined in Control.Carrier.State.Lazy

Methods

empty :: StateC s m a

(<|>) :: StateC s m a -> StateC s m a -> StateC s m a

some :: StateC s m a -> StateC s m [a]

many :: StateC s m a -> StateC s m [a]

(Alternative m, Monad m) => MonadPlus (StateC s m)

Defined in Control.Carrier.State.Lazy

Methods

mzero :: StateC s m a

mplus :: StateC s m a -> StateC s m a -> StateC s m a

Algebra sig m => Algebra (State s :+: sig) (StateC s m)

Defined in Control.Carrier.State.Lazy

Methods

alg :: Functor ctx => Handler ctx n (StateC s m) -> (State s :+: sig) n a -> ctx () -> StateC s m (ctx a)

State effect

module Control.Effect.State