Control.Effect.State

Documentation

type EffectState s es = (Member (State s) es, s ~ StateType es)

data State s a

An effect where a state value is threaded throughout the computation.

Instances

Functor (State s)

runState :: s -> Effect (State s : es) a -> Effect es (a, s)

Completely handles a State effect by providing an initial state, and making the final state explicit.

evalState :: s -> Effect (State s : es) a -> Effect es a

Completely handles a State effect, and discards the final state.

execState :: s -> Effect (State s : es) a -> Effect es s

Completely handles a State effect, and discards the final value.

get :: EffectState s es => Effect es s

Gets the current state.

gets :: EffectState s es => (s -> a) -> Effect es a

Gets a value that is a function of the current state.

put :: EffectState s es => s -> Effect es ()

Replaces the current state.

modify :: EffectState s es => (s -> s) -> Effect es ()

Applies a pure modifier to the state value.

modify' :: EffectState s es => (s -> s) -> Effect es ()

Applies a pure modifier to the state value. The modified value is converted to weak head normal form.

state :: EffectState s es => (s -> (a, s)) -> Effect es a

Lifts a stateful computation to the Effect monad.

withState :: EffectState s es => (s -> s) -> Effect es a -> Effect es a

Runs a computation with a modified state value.

withState f x = modify f >> x