Control.Eff.State.Strict

Strict state effect

Example: implementing Fresh

runFresh' :: (Typeable i, Enum i, Num i) => Eff (Fresh i :> r) w -> i -> Eff r w
runFresh' m s = fst <$> runState s (loop $ admin m)
 where
  loop (Val x) = return x
  loop (E u)   = case decomp u of
    Right (Fresh k) -> do
                      n <- get
                      put (n + 1)
                      loop (k n)
    Left u' -> send (\k -> unsafeReUnion $ k <$> u') >>= loop

Documentation

data State s w

Strict state effect

Constructors

State (s -> s) (s -> w)

Instances

Functor (State s)

Typeable (* -> * -> *) State

get :: (Typeable e, Member (State e) r) => Eff r e

Return the current value of the state.

put :: (Typeable e, Member (State e) r) => e -> Eff r ()

Write a new value of the state.

modify :: (Typeable s, Member (State s) r) => (s -> s) -> Eff r ()

Transform the state with a function.

runState

Arguments

:: Typeable s

=> s

Initial state

-> Eff (State s :> r) w

Effect incorporating State

-> Eff r (s, w)

Effect containing final state and a return value

Run a State effect.

evalState :: Typeable s => s -> Eff (State s :> r) w -> Eff r w

Run a State effect, discarding the final state.

execState :: Typeable s => s -> Eff (State s :> r) w -> Eff r s

Run a State effect and return the final state.