2008/9/30 Galchin, Vasili :

Hello,

I would like to read

1) pedagogical examples of State monad and the Continuation monad

2) library usage of these monads ....

Regarding 1), there is a lot to find on the web. Maybe start on haskell.org. In term of example, here is one I like : ----✁---------------------------------- module StateExample where import Control.Monad.State -- The state : it is threaded along each -- command in MyMonad. type MyState = Int -- A particular use of the State monad : -- simply to wrap a value of type MyState. type MyMonad a = State MyState a -- Inc increments the state. -- The get function retrieves the state -- and the put function replaces it. -- The () in :: MyMonad () means that -- inc doesn't return any (meaningful) -- value. It just has a side effect (it changes -- the wrapped state). -- get has type MyMonad MyState and -- put has type MyState -> MyMonad (). inc :: MyMonad () inc = do v <- get put (v + 1) -- Example usage of the State monad with -- runState (see the docs for other such functions)). -- It starts with the value 5 as the wrapped state. -- THe it performs three times the 'inc' command. -- Thus it produces 8 as the new state. -- As noted aboved, it also returns (). -- Try it in GHCi. Change the {...} and use -- get and put. Implement something else than -- the inc function. example = runState (do {inc ; inc ; inc}) 5 ----✁---------------------------------- Cheers, Thu

Galchin, Vasili wrote:

1) pedagogical examples of State monad and the Continuation monad

Shameless plug: http://www.vex.net/~trebla/haskell/ContMonad.lhs