Control.Monad.Representable.State

adjunctions-4.3: Adjunctions and representable functors

Copyright | (c) Edward Kmett & Sjoerd Visscher 2011
License | BSD3
Maintainer | ekmett@gmail.com
Stability | experimental
Safe Haskell | None
Language | Haskell98

Control.Monad.Representable.State

Description

A generalized State monad, parameterized by a Representable functor. The representation of that functor serves as the state.

Synopsis

- type State g = StateT g Identity
- runState :: Representable g => State g a -> Rep g -> (a, Rep g)
- evalState :: Representable g => State g a -> Rep g -> a
- execState :: Representable g => State g a -> Rep g -> Rep g
- mapState :: Functor g => ((a, Rep g) -> (b, Rep g)) -> State g a -> State g b
- newtype StateT g m a = StateT {
  - getStateT :: g (m (a, Rep g))
  }
- stateT :: Representable g => (Rep g -> m (a, Rep g)) -> StateT g m a
- runStateT :: Representable g => StateT g m a -> Rep g -> m (a, Rep g)
- evalStateT :: (Representable g, Monad m) => StateT g m a -> Rep g -> m a
- execStateT :: (Representable g, Monad m) => StateT g m a -> Rep g -> m (Rep g)
- mapStateT :: Functor g => (m (a, Rep g) -> n (b, Rep g)) -> StateT g m a -> StateT g n b
- liftCallCC :: Representable g => ((((a, Rep g) -> m (b, Rep g)) -> m (a, Rep g)) -> m (a, Rep g)) -> ((a -> StateT g m b) -> StateT g m a) -> StateT g m a
- liftCallCC' :: Representable g => ((((a, Rep g) -> m (b, Rep g)) -> m (a, Rep g)) -> m (a, Rep g)) -> ((a -> StateT g m b) -> StateT g m a) -> StateT g m a
- class Monad m => MonadState s m | m -> s where
  - get :: m s
  - put :: s -> m ()
  - state :: (s -> (a, s)) -> m a

# Documentation

type State g = StateT g Identity

A memoized state monad parameterized by a representable functor `g`, where the representatation of `g`, `Rep g` is the state to carry.

The `return` function leaves the state unchanged, while `>>=` uses the final state of the first computation as the initial state of the second.

runState

Arguments

:: Representable g |
=> State g a | state-passing computation to execute
-> Rep g | initial state
-> (a, Rep g) | return value and final state

Unwrap a state monad computation as a function. (The inverse of `state`.)

evalState

Arguments

:: Representable g |
=> State g a | state-passing computation to execute
-> Rep g | initial value
-> a | return value of the state computation

Evaluate a state computation with the given initial state and return the final value, discarding the final state.

-     evalState m s = fst (runState m s)

execState

Arguments

:: Representable g |
=> State g a | state-passing computation to execute
-> Rep g | initial value
-> Rep g | final state

Evaluate a state computation with the given initial state and return the final state, discarding the final value.

-     execState m s = snd (runState m s)

mapState :: Functor g => ((a, Rep g) -> (b, Rep g)) -> State g a -> State g b

Map both the return value and final state of a computation using the given function.

-     runState (mapState f m) = f . runState m

newtype StateT g m a

A state transformer monad parameterized by:

- `g` - A representable functor used to memoize results for a state `Rep g`
- `m` - The inner monad.

The `return` function leaves the state unchanged, while `>>=` uses the final state of the first computation as the initial state of the second.

Constructors

StateT |
Fields getStateT :: g (m (a, Rep g))

Instances

(Functor f, Representable g, MonadFree f m) => MonadFree f (StateT g m) |
(Representable g, MonadReader e m) => MonadReader e (StateT g m) |
(Representable g, Monad m, (~) * (Rep g) s) => MonadState s (StateT g m) |
(Representable g, MonadWriter w m) => MonadWriter w (StateT g m) |
Representable f => MonadTrans (StateT f) |
Representable f => BindTrans (StateT f) |
(Representable g, Monad m) => Monad (StateT g m) |
(Functor g, Functor m) => Functor (StateT g m) |
(Representable g, Functor m, Monad m) => Applicative (StateT g m) |
(Representable g, MonadCont m) => MonadCont (StateT g m) |
(Representable g, Bind m) => Apply (StateT g m) |
(Representable g, Bind m) => Bind (StateT g m) |

stateT :: Representable g => (Rep g -> m (a, Rep g)) -> StateT g m a

runStateT :: Representable g => StateT g m a -> Rep g -> m (a, Rep g)

evalStateT :: (Representable g, Monad m) => StateT g m a -> Rep g -> m a

Evaluate a state computation with the given initial state and return the final value, discarding the final state.

-     evalStateT m s = liftM fst (runStateT m s)

execStateT :: (Representable g, Monad m) => StateT g m a -> Rep g -> m (Rep g)

Evaluate a state computation with the given initial state and return the final state, discarding the final value.

-     execStateT m s = liftM snd (runStateT m s)

mapStateT :: Functor g => (m (a, Rep g) -> n (b, Rep g)) -> StateT g m a -> StateT g n b

liftCallCC :: Representable g => ((((a, Rep g) -> m (b, Rep g)) -> m (a, Rep g)) -> m (a, Rep g)) -> ((a -> StateT g m b) -> StateT g m a) -> StateT g m a

Uniform lifting of a `callCC` operation to the new monad. This version rolls back to the original state on entering the continuation.

liftCallCC' :: Representable g => ((((a, Rep g) -> m (b, Rep g)) -> m (a, Rep g)) -> m (a, Rep g)) -> ((a -> StateT g m b) -> StateT g m a) -> StateT g m a

In-situ lifting of a `callCC` operation to the new monad. This version uses the current state on entering the continuation. It does not satisfy the laws of a monad transformer.

class Monad m => MonadState s m | m -> s where

Minimal definition is either both of `get` and `put` or just `state`

Minimal complete definition

state | get, put

Methods

get :: m s

Return the state from the internals of the monad.

put :: s -> m ()

Replace the state inside the monad.

state :: (s -> (a, s)) -> m a

Embed a simple state action into the monad.

Instances

MonadState s m => MonadState s (MaybeT m) |
MonadState s m => MonadState s (ListT m) |
MonadState s m => MonadState s (IdentityT m) |
(Functor m, MonadState s m) => MonadState s (Free m) |
(Representable g, Monad m, (~) * (Rep g) s) => MonadState s (StateT g m) |
(Monoid w, MonadState s m) => MonadState s (WriterT w m) |
(Monoid w, MonadState s m) => MonadState s (WriterT w m) |
Monad m => MonadState s (StateT s m) |
Monad m => MonadState s (StateT s m) |
MonadState s m => MonadState s (ReaderT r m) |
MonadState s m => MonadState s (ExceptT e m) |
(Error e, MonadState s m) => MonadState s (ErrorT e m) |
MonadState s m => MonadState s (ContT r m) |
(Monad m, Monoid w) => MonadState s (RWST r w s m) |
(Monad m, Monoid w) => MonadState s (RWST r w s m) |