On Tue, Oct 11, 2011 at 2:37 PM, Brandon Simmons
I'm happy to announce the release of my library 'simple-actors', a DSL-style library for more structured concurrent programs based on the Actor Model. It offers an alternative to ad-hoc use of Chans that allows for tight control of side-effects and message passing, and is especially suited to applications such as simulations of communicating processes.
Pretty interesting!
Here is an example of a system of actors working as a binary tree, supporting insert and query operations: [snip]
I'm kind of spoiled after having used Haskell for a long time, so I couldn't ignore the fact that your example is tied to Ints and don't store a value =). So I've changed the example, as seen below. It's somewhat more complex, but I like the fact that now 'branch' has to deal with updating the value of its key =). -----8<-----BEGIN-EXAMPLE-----8<---- module Main where import Control.Concurrent.Actors import Control.Applicative import Control.Concurrent.MVar type Node k v = Mailbox (Operation k v) -- operations supported by the network: data Operation k v = Insert { key :: k , val :: v } | Query { key :: k , sigVar :: MVar (Maybe v) } -- the actor equivalent of a Nil leaf node: nil :: Ord k => Behavior (Operation k v) nil = Receive $ do (Query _key var) <- received send var Nothing -- signal that key is not present in tree return nil -- await next message <|> do -- else, Insert received l <- spawn nil -- spawn child nodes r <- spawn nil (Insert key val) <- received return $ branch l r key val -- create branch from inserted val -- a "branch" node with a key-value pair and two children branch :: Ord k => Node k v -> Node k v -> k -> v -> Behavior (Operation k v) branch l r k = go where go v = Receive $ do m <- received case compare (key m) k of LT -> send l m >> cont v GT -> send r m >> cont v EQ -> case m of (Query _ var) -> send var (Just v) >> cont v (Insert _ val) -> cont val cont = return . go insert :: Node k v -> (k, v) -> IO () insert t (k,v) = send t (Insert k v) -- MVar is in the 'SplitChan' class so actors can 'send' to it: query :: Node k v -> k -> IO (Maybe v) query t k = do v <- newEmptyMVar send t (Query k v) takeMVar v main :: IO () main = do t <- spawn nil mapM_ (insert t) [(5, "five"), (3, "three"), (7, "seven"), (2, "two"), (4, "four"), (6, "six"), (8, "eight"), (5, "BOO!")] mapM (query t) [1,2,5,7] >>= print -----8<-----END-EXAMPLE-----8<---- Cheers, -- Felipe.