Moduleextensible-effects-5.0.0.1Haskell2010

Control.Eff.State.Lazy

Lazy state effect

3 types
10 values

Packageextensible-effects-5.0.0.1
Exports13
LanguageHaskell2010
LicenceMIT
SourceLazy.hs

datadata State s v where

State, lazy

Initial design: The state request carries with it the state mutator function We can use this request both for mutating and getting the state. But see below for a better design!

data State s v where
  State :: (s->s) -> State s s

In this old design, we have assumed that the dominant operation is modify. Perhaps this is not wise. Often, the reader is most nominant.

See also below, for decomposing the State into Reader and Writer!

The conventional design of State

Constructors

Get :: State s s
Put :: s -> State s ()

Instances3MonadBaseControl, Handle, StM

(MonadBase m m, LiftedBase m r) => MonadBaseControl m (Eff (State s ': r))Defined in extensible-effects-5.0.0.1 · Control.Eff.State.Lazy
Handle (State s) r a (s -> k)Defined in extensible-effects-5.0.0.1 · Control.Eff.State.Lazy
Handle 'State s' requests
type StM (Eff (State s ': r)) a = StM (Eff r) (a, s)Defined in extensible-effects-5.0.0.1 · Control.Eff.State.Lazy

valuewithState :: Monad m => a -> s -> m (a, s)

Embed a pure value in a stateful computation, i.e., given an initial state, how to interpret a pure value in a stateful computation.

valueget :: Member (State s) r => Eff r s

Return the current value of the state. The signatures are inferred

valueput :: Member (State s) r => s -> Eff r ()

Write a new value of the state.

valuerunState

:: s
Initial state
-> Eff (State s ': r) a
Effect incorporating State
-> Eff r (a, s)
Effect containing final state and a return value

Run a State effect

valuemodify :: Member (State s) r => (s -> s) -> Eff r ()

Transform the state with a function.

valueevalState :: s -> Eff (State s ': r) a -> Eff r a

Run a State effect, discarding the final state.

valueexecState :: s -> Eff (State s ': r) a -> Eff r s

Run a State effect and return the final state.

datadata TxState (s :: k) (v :: k) where

An encapsulated State handler, for transactional semantics The global state is updated only if the transactionState finished successfully

Constructors

TxState :: TxState s s

typetype TxStateT (s :: k) = TxState s s

valuewithTxState :: Member (State s) r => a -> s -> Eff r a

Embed Transactional semantics to a stateful computation.

valuetransactionState :: Member (State s) r => TxStateT s -> Eff r a -> Eff r a

Confer transactional semantics on a stateful computation.

valuerunStateR :: s -> Eff (Writer s ': Reader s ': r) a -> Eff r (a, s)

A different representation of State: decomposing State into mutation (Writer) and Reading. We don't define any new effects: we just handle the existing ones. Thus we define a handler for two effects together.