Control.Monad.Freer.StateRW

Composable handler for State effects in terms of Reader and Writer effects. This module is more a tutorial on how to compose handlers. It is slightly slower than a dedicated State handler.

Using http://okmij.org/ftp/Haskell/extensible/Eff1.hs as a starting point.

Documentation

runStateR :: Eff (Writer s ': (Reader s ': effs)) a -> s -> Eff effs (a, s)

State handler, using Reader and Writer effects.

data Reader e a

Represents shared immutable environment of type (e :: *) which is made available to effectful computation.

data Writer w a

Writer effects - send outputs to an effect environment.

tell :: Member (Writer w) effs => w -> Eff effs ()

Send a change to the attached environment.

ask :: Member (Reader e) effs => Eff effs e

Request a value of the environment.