mtl-2.2.2: Monad classes, using functional dependencies

Description

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.

Synopsis

# Documentation

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

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

Minimal complete definition

Methods

get :: m s Source #

Return the state from the internals of the monad.

put :: s -> m () Source #

Replace the state inside the monad.

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

Embed a simple state action into the monad.

Instances

modify :: MonadState s m => (s -> s) -> m () Source #

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.