Copyright | (c) Edward Kmett & Sjoerd Visscher 2011 |
---|---|

License | BSD3 |

Maintainer | ekmett@gmail.com |

Stability | experimental |

Safe Haskell | None |

Language | Haskell98 |

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

- 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 {}
- 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

# Documentation

type State g = StateT g Identity Source

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.

:: 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`

.)

:: Representable g | |

=> State g a | state-passing computation to execute |

-> Rep g | initial value |

-> a | return value of the state computation |

:: Representable g | |

=> State g a | state-passing computation to execute |

-> Rep g | initial value |

-> Rep g | final state |

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.

(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) |

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

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) Source

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)

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 Source

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 Source

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`

Nothing

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.

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) | |

(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) |