| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Polysemy.State
Synopsis
- data State s m a where
- get :: forall s r. MemberWithError (State s) r => Sem r s
- gets :: forall s a r. Member (State s) r => (s -> a) -> Sem r a
- put :: forall s r. MemberWithError (State s) r => s -> Sem r ()
- modify :: Member (State s) r => (s -> s) -> Sem r ()
- modify' :: Member (State s) r => (s -> s) -> Sem r ()
- runState :: s -> Sem (State s ': r) a -> Sem r (s, a)
- evalState :: s -> Sem (State s ': r) a -> Sem r a
- execState :: s -> Sem (State s ': r) a -> Sem r s
- runLazyState :: s -> Sem (State s ': r) a -> Sem r (s, a)
- evalLazyState :: s -> Sem (State s ': r) a -> Sem r a
- execLazyState :: s -> Sem (State s ': r) a -> Sem r s
- runStateIORef :: forall s r a. Member (Embed IO) r => IORef s -> Sem (State s ': r) a -> Sem r a
- stateToIO :: forall s r a. Member (Embed IO) r => s -> Sem (State s ': r) a -> Sem r (s, a)
- runStateSTRef :: forall s st r a. Member (Embed (ST st)) r => STRef st s -> Sem (State s ': r) a -> Sem r a
- stateToST :: forall s st r a. Member (Embed (ST st)) r => s -> Sem (State s ': r) a -> Sem r (s, a)
- hoistStateIntoStateT :: Sem (State s ': r) a -> StateT s (Sem r) a
Effect
data State s m a where Source #
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.
Instances
| type DefiningModule (State :: Type -> k -> Type -> Type) Source # | |
Defined in Polysemy.State | |
Actions
modify' :: Member (State s) r => (s -> s) -> Sem r () Source #
A variant of modify in which the computation is strict in the
new state.
Interpretations
evalState :: s -> Sem (State s ': r) a -> Sem r a Source #
Run a State effect with local state.
Since: 1.0.0.0
execState :: s -> Sem (State s ': r) a -> Sem r s Source #
Run a State effect with local state.
Since: 1.2.3.1
runLazyState :: s -> Sem (State s ': r) a -> Sem r (s, a) Source #
Run a State effect with local state, lazily.
evalLazyState :: s -> Sem (State s ': r) a -> Sem r a Source #
Run a State effect with local state, lazily.
Since: 1.0.0.0
execLazyState :: s -> Sem (State s ': r) a -> Sem r s Source #
Run a State effect with local state, lazily.
Since: 1.2.3.1
runStateIORef :: forall s r a. Member (Embed IO) r => IORef s -> Sem (State s ': r) a -> Sem r a Source #
Run a State effect by transforming it into operations over an IORef.
Note: This is not safe in a concurrent setting, as modify isn't atomic.
If you need operations over the state to be atomic,
use runAtomicStateIORef or
runAtomicStateTVar instead.
Since: 1.0.0.0
stateToIO :: forall s r a. Member (Embed IO) r => s -> Sem (State s ': r) a -> Sem r (s, a) Source #
Run an State effect in terms of operations
in IO.
Internally, this simply creates a new IORef, passes it to
runStateIORef, and then returns the result and the final value
of the IORef.
Note: This is not safe in a concurrent setting, as modify isn't atomic.
If you need operations over the state to be atomic,
use atomicStateToIO instead.
Beware: As this uses an IORef internally,
all other effects will have local
state semantics in regards to State effects
interpreted this way.
For example, throw and catch will
never revert puts, even if runError is used
after stateToIO.
Since: 1.2.0.0
runStateSTRef :: forall s st r a. Member (Embed (ST st)) r => STRef st s -> Sem (State s ': r) a -> Sem r a Source #
stateToST :: forall s st r a. Member (Embed (ST st)) r => s -> Sem (State s ': r) a -> Sem r (s, a) Source #
Run an State effect in terms of operations
in ST.
Internally, this simply creates a new STRef, passes it to
runStateSTRef, and then returns the result and the final value
of the STRef.
Beware: As this uses an STRef internally,
all other effects will have local
state semantics in regards to State effects
interpreted this way.
For example, throw and catch will
never revert puts, even if runError is used
after stateToST.
When not using the plugin, one must introduce the existential st type to
stateToST, so that the resulting type after runM can be resolved into
forall st. ST st (s, a) for use with runST. Doing so requires
-XScopedTypeVariables.
stResult :: forall s a. (s, a) stResult = runST ( (runM $ stateToST @_ @st undefined $ pure undefined) :: forall st. ST st (s, a) )
Since: 1.3.0.0