Control.Monad.State.Class
| Copyright | (c) Andy Gill 2001 (c) Oregon Graduate Institute of Science and Technology 2001 |
|---|---|
| License | BSD-style (see the file LICENSE) |
| Maintainer | [email protected] |
| Stability | experimental |
| Portability | non-portable (multi-param classes, functional dependencies) |
| Safe Haskell | Safe |
| Language | Haskell2010 |
Description
MonadState class.
This module is inspired by the paper Functional Programming with Overloading and Higher-Order Polymorphism, Mark P Jones (http://web.cecs.pdx.edu/~mpj/) Advanced School of Functional Programming, 1995.
class Monad m => MonadState s m | m -> s where Source
Minimal definition is either both of get and put or just state
Methods
Return the state from the internals of the monad.
Replace the state inside the monad.
state :: (s -> (a, s)) -> m a Source
Embed a simple state action into the monad.
Instances
| MonadState s m => MonadState s (MaybeT m) | |
| MonadState s m => MonadState s (ListT m) | |
| (Monoid w, MonadState s m) => MonadState s (WriterT w m) | |
| (Monoid w, MonadState s m) => MonadState s (WriterT w m) | |
| MonadState s m => MonadState s (ReaderT r m) | |
| MonadState s m => MonadState s (IdentityT m) | |
| MonadState s m => MonadState s (ExceptT e m) | Since: mtl-2.2 |
| (Error e, MonadState s m) => MonadState s (ErrorT e m) | |
| Monad m => MonadState s (StateT s m) | |
| Monad m => MonadState s (StateT s 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) | |
modify :: MonadState s m => (s -> s) -> m () Source
Monadic state transformer.
Maps an old state to a new state inside a state monad. The old state is thrown away.
Main> :t modify ((+1) :: Int -> Int)
modify (...) :: (MonadState Int a) => a ()
This says that modify (+1) acts over any Monad that is a member of the MonadState class, with an Int state.
modify' :: MonadState s m => (s -> s) -> m () Source
A variant of modify in which the computation is strict in the new state.
Since: mtl-2.2
gets :: MonadState s m => (s -> a) -> m a Source
Gets specific component of the state, using a projection function supplied.
© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).
https://downloads.haskell.org/~ghc/8.10.2/docs/html/libraries/mtl-2.2.2/Control-Monad-State-Class.html