| 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 |
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
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.
| 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/8.8.3/docs/html/libraries/mtl-2.2.2/Control-Monad-State-Class.html