GHC 10.0.0.20260917 · lts/ghc-10.0.x · 8fef28d · 2026-11-02
Moduleeffectful-core-2.7.1.2GHC2021
Support for access to a mutable value of a particular type.
The value is thread local. If you want it to be shared between threads, use Effectful.State.Static.Shared.
Note: unlike the Control.Monad.Trans.State.StateT monad transformer from
the transformers library, the State effect doesn't discard state updates
when an exception is received:
import Control.Exception (ErrorCall)import Control.Monad.Catchimport Control.Monad.Trans.State.Strict qualified as S
:{ (`S.execStateT` "Hi") . handle (\(_::ErrorCall) -> pure ()) $ do S.modify (++ " there!") error "oops":}"Hi"
:{ runEff . execState "Hi" . handle (\(_::ErrorCall) -> pure ()) $ do modify (++ " there!") error "oops":}"Hi there!"
Provide access to a strict (WHNF), thread local, mutable value of type s.
type DispatchOf (State s) = 'Static 'NoSideEffectsDefined in effectful-core-2.7.1.2 · Effectful.State.Static.Localdata StaticRep (State s)State sRun the State effect with the given initial state and return the final value along with the final state.
Run the State effect with the given initial state and return the final value, discarding the final state.
Run the State effect with the given initial state and return the final state, discarding the final value.
Fetch the current value of the state.
Set the current state to the given value.
state :: (HasCallStack, State s :> es)=> (s -> (a, s))The function to modify the state.
-> Eff es aApply the function to the current state and return a value.
modify :: (HasCallStack, State s :> es)=> (s -> s)The function to modify the state.
-> Eff es ()stateM :: (HasCallStack, State s :> es)=> (s -> Eff es (a, s))The function to modify the state.
-> Eff es aDeprecated. State modifications made via operations of the same State effect within the callback are discarded. Use a combination of get and put instead.
Apply the monadic function to the current state and return a value.