| Copyright | (c) 2021 Xy Ren |
|---|---|
| License | BSD3 |
| Maintainer | xy.r@outlook.com |
| Stability | experimental |
| Portability | non-portable (GHC only) |
| Safe Haskell | Trustworthy |
| Language | Haskell2010 |
Cleff.State
Contents
Description
Synopsis
- data State s :: Effect where
- get :: State s :> es => Eff es s
- put :: State s :> es => s -> Eff es ()
- state :: State s :> es => (s -> (a, s)) -> Eff es a
- gets :: State s :> es => (s -> t) -> Eff es t
- modify :: State s :> es => (s -> s) -> Eff es ()
- runState :: s -> Eff (State s ': es) a -> Eff es (a, s)
- runStateIORef :: IOE :> es => IORef s -> Eff (State s ': es) a -> Eff es a
- runStateMVar :: IOE :> es => MVar s -> Eff (State s ': es) a -> Eff es a
- runStateTVar :: IOE :> es => TVar s -> Eff (State s ': es) a -> Eff es a
- zoom :: State t :> es => Lens' t s -> Eff (State s ': es) ~> Eff es
Effect
data State s :: Effect where Source #
An effect capable of providing a mutable state s that can be read and written. This roughly corresponds to the
MonadState typeclass and StateT monad transformer in the mtl library.
Operations
Arguments
| :: State s :> es | |
| => (s -> (a, s)) | The function that takes the state and returns a result value together with a modified state |
| -> Eff es a |
Modify the state and produce a value from the state via a function.
modify :: State s :> es => (s -> s) -> Eff es () Source #
Modify the value of the state via a function.
Interpretations
runState :: s -> Eff (State s ': es) a -> Eff es (a, s) Source #
Run the State effect.
Caveats
The runState interpreter is implemented with IORefs and there is no way to do arbitrary
atomic transactions. The state operation is atomic though and it is implemented with atomicModifyIORefCAS, which
can be faster than atomicModifyIORef in contention. For any more complicated cases of atomicity, please build your
own effect that uses either MVars or TVars based on your need.
Unlike mtl, in cleff the state will not revert when an error is thrown.
runState will stop taking care of state operations done on forked threads as soon as the main thread finishes its
computation. Any state operation done before main thread finishes is still taken into account.