Polysemy.State

Effect

data State s m a where

An effect for providing statefulness. Note that unlike mtl's StateT, there is no restriction that the State effect corresponds necessarily to local state. It could could just as well be interrpeted in terms of HTTP requests or database access.

Interpreters which require statefulness can reinterpret themselves in terms of State, and subsequently call runState.

Constructors

Get :: State s m s

Put :: s -> State s m ()

Instances

type DefiningModule (State :: Type -> k -> Type -> Type)

Defined in Polysemy.State

type DefiningModule (State :: Type -> k -> Type -> Type) = "Polysemy.State"

Actions

get :: forall a r. Member (State a) r => Sem r a

gets :: Member (State s) r => (s -> a) -> Sem r a

put :: forall s r. Member (State s) r => s -> Sem r ()

modify :: Member (State s) r => (s -> s) -> Sem r ()

Interpretations

runState :: s -> Sem (State s ': r) a -> Sem r (s, a)

Run a State effect with local state.

runLazyState :: s -> Sem (State s ': r) a -> Sem r (s, a)

Run a State effect with local state, lazily.

runStateInIORef :: forall s r a. Member (Lift IO) r => IORef s -> Sem (State s ': r) a -> Sem r a

Run a State effect by transforming it into operations over an IORef.

Since: 0.1.2.0

Interoperation with MTL

hoistStateIntoStateT :: Sem (State s ': r) a -> StateT s (Sem r) a

Hoist a State effect into a StateT monad transformer. This can be useful when writing interpreters that need to interop with MTL.

Since: 0.1.3.0