Control.Monad.MonadStateIO

general usefull state monad for a local state and IO

This module is used for threading a state and io actions through a computation. Here the monad is constructed by hand. It could easily be refactored with the use of the monad transformer library.

Documentation

newtype StateIO state res

Constructors

STIO

Fields

trans :: state -> IO (res, state)

Instances

Monad (StateIO state)

io :: IO a -> StateIO state a

lift IO command to StateIO

trcState :: (state -> String) -> StateIO state ()

state inspection command: a "show"-like function is applied to the state and the result is written to stderr.

changeState :: (state -> state) -> StateIO state state

change the state with a given function and return the new state

setState :: state -> StateIO state state

set the state

getState :: StateIO state state

read the state

run :: state -> StateIO state res -> IO res

run a StateIO command with an initial state