Control.Monad.Levels.State.Lazy

Lazy stateful computations.

Documentation

state :: forall m s a. HasState s m => (s -> (a, s)) -> m a

Embed a simple state action into the monad stack.

get :: HasState s m => m s

Obtain the state environment.

gets :: HasState s m => (s -> a) -> m a

Apply a function to the stateful environment. Equivalent to fmap f get.

put :: HasState s m => s -> m ()

Replace the stateful environment.

modify :: HasState s m => (s -> s) -> m ()

Map the old state to a new state, and discard the old one. Equivalent to gets f >>= put.

modify' :: HasState s m => (s -> s) -> m ()

A variant of modify in which the computation is strict in the new state.

newtype StateT s m a :: * -> (* -> *) -> * -> *

A state transformer monad parameterized by:

• s - The state.
• m - The inner monad.

The return function leaves the state unchanged, while >>= uses the final state of the first computation as the initial state of the second.

Constructors

StateT

Fields

runStateT :: s -> m (a, s)

Instances

MonadTower m => IsState s (StateT s m)

MonadTrans (StateT s)

MonadLevel m => ConstraintPassThrough (IsTransformer (StateT s)) (ListT m) True

MonadLevel m => ConstraintPassThrough (IsTransformer (StateT s)) (ContT r m) True

(Functor m, MonadPlus m) => Alternative (StateT s m)

Monad m => Monad (StateT s m)

Functor m => Functor (StateT s m)

MonadFix m => MonadFix (StateT s m)

MonadPlus m => MonadPlus (StateT s m)

(Functor m, Monad m) => Applicative (StateT s m)

MonadIO m => MonadIO (StateT s m)

MonadTower m => MonadLevel_ (StateT s m)

MonadTower m => MonadTower_ (StateT s m)

type LowerMonad (StateT s m) = m

type WithLower_ (StateT s m) = AddIG

type AllowOtherValues (StateT s m) = True

type DefaultAllowConstraints (StateT s m) = True

type BaseMonad (StateT s m) = BaseMonad m

type InnerValue (StateT s m) a = (a, s)

type HasState s m = SatisfyConstraint (IsState s) m

A monad stack containing a stateful environment of type s.

class MonadTower m => IsState s m

The minimal definition needed for a monad providing a stateful environment.

Instances

MonadTower m => IsState s (StateT s m)

MonadTower m => IsState s (StateT s m)

(MonadTower m, Monoid w) => IsState s (RWST r w s m)

(MonadTower m, Monoid w) => IsState s (RWST r w s m)

ValidConstraint (IsState s)

MonadTower m => ConstraintPassThrough (IsState s) (ListT m) True

MonadTower m => ConstraintPassThrough (IsState s) (ContT r m) True

type ConstraintSatisfied (IsState s) m