
Control.Monad.State.Class  Portability  nonportable (multiparam classes, functional dependencies)  Stability  experimental  Maintainer  libraries@haskell.org 





Description 
MonadState class.
This module is inspired by the paper
/Functional Programming with Overloading and
HigherOrder Polymorphism/,
Mark P Jones (http://web.cecs.pdx.edu/~mpj/)
Advanced School of Functional Programming, 1995.


Synopsis 




MonadState class


class Monad m => MonadState s m  m > s where 
get returns the state from the internals of the monad.
put replaces the state inside the monad.
  Methods  get :: m s   put :: s > m () 
  Instances  


modify :: MonadState s m => (s > s) > m () 
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.


gets :: MonadState s m => (s > a) > m a 
Gets specific component of the state, using a projection function
supplied.


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