packages feed

transient (empty) → 0.1.0.0

raw patch · 10 files changed

+2483/−0 lines, 10 filesdep +HTTPdep +basedep +containerssetup-changed

Dependencies added: HTTP, base, containers, directory, filepath, mtl, network, network-info, process, random, stm, transformers, transient

Files

+ LICENSE view
@@ -0,0 +1,674 @@+              GNU GENERAL PUBLIC LICENSE
+                Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
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+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+              END OF TERMS AND CONDITIONS
+
+     How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<http://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<http://www.gnu.org/philosophy/why-not-lgpl.html>.
+ Main.hs view
@@ -0,0 +1,383 @@+
+
+{-# LANGUAGE ScopedTypeVariables #-}
+
+{-# LANGUAGE DeriveDataTypeable  #-}
+module Main where
+
+import           Data.Typeable
+import           Transient.Base
+import           Transient.Backtrack
+import           Transient.Indeterminism
+import           Transient.Logged
+import           Transient.Move
+import           Transient.EVars
+import           Control.Applicative
+import           Control.Concurrent
+import           Control.Exception
+import           Control.Monad.State
+import           Data.Monoid
+import           System.IO.Unsafe
+import           System.Directory
+import           System.FilePath
+import           Network.HTTP
+import           Network
+import           System.IO
+import           Data.IORef
+
+import Data.List hiding (find,map, group)
+
+
+main= keep $ do
+      oneThread $ option "main" "to kill previous spawned processes and return to the main menu"   <|> return ""
+      liftIO $ putStrLn "MAIN MENU"
+
+      nonDeterminsm <|> trans <|>
+             colors <|> app   <|>
+            futures <|> server <|> 
+            distributed <|> pubSub
+
+solveConstraint=  do
+      x <- choose  [1,2,3]
+      y <- choose  [4,5,6]
+
+      guard $ x * y == 8
+
+      return (x,y)
+
+pythags = freeThreads $ do
+  x <- choose [1..50]
+  y <- choose ([1..x] :: [Int])
+  z <- choose [1..round $ sqrt(fromIntegral $ 2*x*x)]
+
+  guard (x*x+y*y==z*z)
+  th <- liftIO $  myThreadId
+  return (x, y, z, th)
+
+example1= do
+    option "ex1" "example 1"
+    r <- threads 4 solveConstraint
+    liftIO $ print r
+
+example2= do
+    option "pyt" "pythagoras"
+    r<- threads 2 pythags
+    liftIO $ print r
+
+collectSample= threads 4 $ do
+    option "coll" "group sample: return results in a list"
+    r <- collect 0 $ do
+      x <- choose  [1,2,3]
+      y <- choose  [4,5,6]
+      th <- liftIO $ threadDelay 1000 >> myThreadId
+
+      return (x,y,th)
+
+    liftIO $ print r
+
+threadSample= do
+     option "th" "threads sample"
+     liftIO $ print "number of threads? (< 10)"
+
+     n <- input  ( < 10)
+
+     threads n $ do
+        x <- choose  [1,2,3]
+        y <- choose  [4,5,6]
+        th <- liftIO $ myThreadId
+        liftIO $ print (x,y,th)
+
+nonDeterminsm= do
+      option "nondet" "Non determinism examples"
+      example1 <|> example2
+               <|> collectSample
+               <|> threadSample
+               <|> fileSearch
+
+
+
+find' :: String -> FilePath -> TransientIO FilePath
+find' s d = do
+  fs <- liftIO $ getDirectoryContents d
+       `catch` \(e:: SomeException) -> return []       -- 1
+  let fs' = sort $ filter (`notElem` [".",".."]) fs    -- 2
+  if any (== s) fs'                                    -- 3
+     then do
+       liftIO $ print $ d </> s
+       return $ d</> s
+     else do
+       f <- choose fs'                                 -- 4
+       let d' = d </> f                                -- 6
+       isdir <- liftIO $ doesDirectoryExist d'         -- 7
+       if isdir then find' s d'                        -- 8
+                else stop
+
+
+------------------
+
+fileSearch=   do
+    option "file" "example of file search"
+    r<- threads 3 $ collect 10 $ find' "Main.hs"  "."
+    liftIO $ putStrLn $ "SOLUTION= "++ show  r
+--    exit
+
+
+
+
+
+
+
+trans= do
+       option "trans" "transaction examples with backtracking for undoing actions"
+       transaction <|> transaction2
+
+transaction=   do
+       option "back" "backtracking test"
+       productNavigation
+       reserve
+       payment
+
+transaction2= do
+       option "back2" "backtracking test 2"
+       productNavigation
+       reserveAndSendMsg
+       payment
+
+
+       liftIO $ print "done!"
+
+
+productNavigation = liftIO $ putStrLn "product navigation"
+
+reserve= liftIO (putStrLn "product reserved,added to cart")
+                 `onUndo` liftIO (putStrLn "product un-reserved")
+
+payment = do
+           liftIO $ putStrLn "Payment failed"
+           undo
+
+reserveAndSendMsg= do
+            reserve
+            liftIO  (putStrLn "update other database necesary for the reservation")
+                 `onUndo` liftIO (putStrLn "database update undone")
+
+
+
+colors :: TransientIO ()
+colors= do
+       option "colors" "choose between three colors"
+       r <-  color 1  "red"  <|> color 2 "green" <|> color 3 "blue"
+       liftIO $ print r
+       where
+       color :: Int -> String -> TransientIO String
+       color n str= do
+         option (show n) str
+         liftIO . print $ str ++ " color"
+         return  str
+
+app :: TransientIO ()
+app= do
+       option "app" "applicative expression that return a counter in 2-tuples every second"
+       liftIO $ putStrLn "to stop the sequence, write main(enter)"
+       counter <- liftIO $ newMVar 0
+
+       r <-  (,) <$>  number  counter 1 <*> number counter 1
+
+
+       liftIO $ putStrLn $ "result=" ++ show r
+       where
+       number counter n= waitEvents $ do
+          threadDelay $ n * 1000000
+          n <- takeMVar counter
+          putMVar counter (n+1)
+          return n
+
+futures= do
+       option "async" "for parallelization of IO actions with applicative and monoidal combinators"
+       sum1 <|> sum2
+
+sum1 :: TransientIO ()
+sum1= do
+       option "sum1" "access to two web pages concurrently and sum the number of words using Applicative"
+       liftIO $ print " downloading data..."
+       (r,r') <- (,) <$> async  (worker "http://www.haskell.org/")
+                     <*> async  (worker "http://www.google.com/")
+
+       liftIO $ putStrLn $ "result="  ++ show  (r + r')
+
+getURL= simpleHTTP . getRequest
+
+worker :: String -> IO Int
+worker url=do
+      r <- getURL url
+      body <- getResponseBody r
+      putStrLn $ "number of words in " ++ url ++" is: " ++ show(length (words body))
+      return . length . words $ body
+
+sum2 :: TransientIO ()
+sum2= do
+      option "sum2" "access to N web pages concurrenty and sum the number of words using map-fold"
+      liftIO $ print " downloading data..."
+      rs <- foldl (<>) (return 0) $ map (async . worker)
+                  [ "http://www.haskell.org/"
+                  , "http://www.google.com/"]
+
+      liftIO $ putStrLn $ "result="  ++ show rs
+
+instance Monoid Int where
+      mappend= (+)
+      mempty= 0
+
+server :: TransientIO ()
+server=  do
+       option "server" "A web server in the port 8080"
+       liftIO $ print "Server Stated"
+       sock <-  liftIO $  listenOn $ PortNumber 8080
+
+       (h,_,_) <- spawn $ accept sock `catch` (\(e::SomeException) -> sClose sock >> throw e)
+       liftIO $ do
+           hPutStr h msg
+           putStrLn "new request"
+           hFlush h
+           hClose h
+         `catch` (\(e::SomeException) -> sClose sock)
+
+msg = "HTTP/1.0 200 OK\r\nContent-Length: 5\r\n\r\nPong!\r\n"
+
+
+-- distributed computing
+
+distributed= do
+      option "distr" "examples of distributed computing"
+      let port1 = PortNumber 2000
+
+
+      addNodes [Node host port1 Nothing]
+      listen port1 <|> return ()-- conn port1 port1 <|> conn port2 port1
+
+      examples' host port1
+      where
+      host= "localhost"
+      conn p p'=  connect host p host p'
+
+examples' remoteHost remotePort= do
+   logged $ option "maind"  "to see this menu" <|> return ""
+   r <-logged    $ option "move" "move to another node"
+               <|> option "call" "call a function in another node"
+               <|> option "chat" "chat"
+               <|> option "netev" "events propagating trough the network"
+   case r of
+       "call"  -> callExample remoteHost remotePort
+       "move"  -> moveExample remoteHost remotePort
+       "chat"  -> chat
+       "netev" -> networkEvents remoteHost remotePort
+
+
+callExample host port= do
+   logged $ putStrLnhp  port "asking for the remote data"
+   s <- callTo host port $ liftIO $ do
+                       putStrLnhp  port "remote callTo request"
+                       readIORef environ
+
+
+   liftIO $ putStrLn $ "resp=" ++ show s
+
+
+environ= unsafePerformIO $ newIORef "Not Changed"
+
+moveExample host port= do
+   putStrLnhp  port "enter a string. It will be inserted in the other node by a migrating program"
+   name <- logged $ input (const True)
+   beamTo host port
+   putStrLnhp  port "moved!"
+   putStrLnhp  port $ "inserting "++ name ++" as new data in this node"
+   liftIO $ writeIORef environ name
+   return()
+
+
+chat ::  TransIO ()
+chat  = do
+    name  <- logged $ do liftIO $ putStrLn "Name?" ; input (const True)
+    text <- logged $  waitEvents  $ putStr ">" >> hFlush stdout >> getLine' (const True)
+    let line= name ++": "++ text
+    clustered $   liftIO $ putStrLn line
+
+
+networkEvents rh rp= do
+     logged $  do
+       putStrLnhp  rp "callTo is not  a simole remote call. it stablish a connection"
+       putStrLnhp  rp "between transient processes in different nodes"
+       putStrLnhp  rp "in this example, events are piped back from a remote node to the local node"
+
+     r <- callTo rh rp $ do
+                         option "fire"  "fire event"
+                         return "event fired"
+     putStrLnhp  rp $ r ++ " in remote node"
+
+putStrLnhp p msg= liftIO $ putStr (show p) >> putStr " ->" >> putStrLn msg
+
+
+pubSub=  do
+  option "pubs" "an example of publish-subscribe using Event Vars (EVars)"
+  v <- newEVar  :: TransIO (EVar String)
+  v' <- newEVar 
+  suscribe v v' <|> publish v v'
+  where 
+      
+  publish v v'= do
+    liftIO $ putStrLn "Enter a message to publish"
+    msg <- input(const True)
+    writeEVar v msg
+    liftIO $ putStrLn "after writing first EVar\n"
+    writeEVar v' $ "second " ++ msg
+    liftIO $ putStrLn "after writing second EVar\n"
+    publish v v'
+    
+  suscribe :: EVar String -> EVar String -> TransIO ()
+  suscribe v v'= do
+       r <- (,) <$> proc1 v  <*>  proc2 v'
+       liftIO $ do
+             putStr $ "applicative result= " 
+             print r
+
+  suscribe2 ::  EVar String -> EVar String -> TransIO ()
+  suscribe2 v v'= do
+        x <- readEVar v
+        y <- readEVar v'
+        liftIO $ do
+                 putStr "monadic result"
+                 print (x,y)
+
+  proc1 v=  do
+    msg <- readEVar v 
+    liftIO $ putStrLn $  "proc1 readed var: " ++ show msg
+    return msg
+    
+  proc2 v= do
+    msg <- readEVar v
+    liftIO $ putStrLn $ "proc2 readed var: " ++ show msg
+    return msg
+
+
+
+
+
+
+--main=do
+--      r <- getURL "https://www.w3.org/services/html2txt?url=http%3A%2F%2Fwww.searchquotes.com%2Fsearch%2Ftransient%2F"
+--      body <- getResponseBody r
+--      print $ parse  quote' "" body
+--      where
+--      quote'= do
+--          q <-  between(brackets natural) (brackets natural) string
+--
+--          if "http" `isPrefixOf` q
+--            then quote'
+--            else  return q
+--
+
+--main    = case (parse numbers "" "11, 2, 43") of
+--            Left err  -> print err
+--            Right xs  -> print (sum xs)
+--
+--numbers = commaSep integer
+ Setup.hs view
@@ -0,0 +1,2 @@+import Distribution.Simple
+main = defaultMain
+ move.hs view
@@ -0,0 +1,185 @@+{-# LANGUAGE ScopedTypeVariables, DeriveDataTypeable #-}
+module Main where
+
+import Transient.Move
+import Transient.Logged
+import Transient.Base
+import Network
+import Control.Applicative
+
+import Control.Monad.IO.Class
+import System.Environment
+import System.IO.Unsafe
+import Data.Monoid
+import System.IO
+import Control.Monad
+import Data.Maybe
+import Control.Exception
+import Control.Concurrent (threadDelay)
+import Data.Typeable
+import Control.Concurrent.STM
+import Data.IORef
+
+
+main= do
+      let port1 = PortNumber 2000
+          port2 = PortNumber 2001
+
+
+      keep $  do
+        conn port1 port1 <|> conn port2 port1
+
+        examples' host port2
+      where
+      host= "localhost"
+--      delay = liftIO $ threadDelay 1000000
+      conn p p'=  connect host p host p'
+
+
+
+
+
+test = do
+   args <- getArgs
+   let ports= [("localhost",PortNumber 2000), ("localhost",PortNumber 2001)]
+
+   let [(_,port1), (_,port2)]= if null args  then ports else reverse ports
+   print [port1, port2]
+   let local= "localhost"
+   beamInit port1 $ do
+           logged $ option "call" "call"
+           callTo local port2 (liftIO $ print "HOLA")
+             <|> callTo local port2(liftIO $ print "HELLO")
+
+
+
+two = do
+  args <- getArgs
+  if length args < 2
+    then do
+     putStrLn "The program need at least two parameters:  localHost localPort  remoteHost RemotePort"
+     putStrLn "Start one node alone. The rest, connected to this node."
+     return ()
+    else keep $ do
+       let localHost= head args
+           localPort= PortNumber . fromInteger . read $ args !! 1
+           (remoteHost,remotePort) =
+             if length args >=4
+                then(args !! 2, PortNumber . fromInteger . read $ args !! 3)
+                else (localHost,localPort)
+       connect localHost localPort remoteHost remotePort
+       examples
+
+
+examples = do
+   nodes <- logged getNodes
+   logged $ liftIO $ print $ "NODES=" ++ show  nodes
+   let (remoteHost,remotePort)=  head $ tail nodes
+   examples' remoteHost remotePort
+
+examples' remoteHost remotePort= do
+   logged $ option "main"  "to see the menu" <|> return ""
+   r <-logged      $ option "move" "move to another node"
+               <|> option "call" "call a function in another node"
+               <|> option "chat" "chat"
+               <|> option "netev" "events propagating trough the network"
+   case r of
+       "call" -> callExample remoteHost remotePort
+       "move" -> moveExample remoteHost remotePort
+       "chat" -> chat
+       "netev" -> networkEvents remoteHost remotePort
+
+data Environ= Environ (IORef String) deriving Typeable
+
+callExample host port= do
+   logged $ putStrLnhp  port "asking for the remote data"
+   s <- callTo host port $  do
+                       putStrLnhp  port "remote callTo request"
+                       Environ environ <- getSData <|> do
+                                    ref <- liftIO $ newIORef "Not Changed"
+                                    let env= Environ ref
+                                    setSData env
+                                    return env
+                       liftIO $ readIORef environ
+
+
+   liftIO $ putStrLn $ "resp=" ++ show s
+
+
+environ= unsafePerformIO $ newIORef "Not Changed"
+
+moveExample host port= do
+   putStrLnhp  port "enter a string. It will be inserted in the other node by a migrating program"
+   name <- logged $ input (const True)
+   beamTo host port
+   putStrLnhp  port "moved!"
+   putStrLnhp  port $ "inserting "++ name ++" as new data in this node"
+   Environ environ <- getSData <|> do
+                                    ref <- liftIO $ newIORef "Not Changed"
+                                    let env= Environ ref
+                                    setSData env
+                                    return env
+
+   liftIO $ writeIORef environ name
+   return()
+
+
+chat ::  TransIO ()
+chat  = do
+    name  <- logged $ do liftIO $ putStrLn "Name?" ; input (const True)
+    text <- logged $  waitEvents  $ putStr ">" >> hFlush stdout >> getLine' (const True)
+    let line= name ++": "++ text
+    clustered $   liftIO $ putStrLn line
+
+
+networkEvents rh rp= do
+     logged $  do
+       putStrLnhp  rp "callTo is not  a simole remote call. it stablish a connection"
+       putStrLnhp  rp "between transient processes in different nodes"
+       putStrLnhp  rp "in this example, events are piped back from a remote node to the local node"
+
+     r <- callTo rh rp $ do
+                         option "fire"  "fire event"
+                         return "event fired"
+     putStrLnhp  rp $ r ++ " in remote node"
+
+putStrLnhp p msg= liftIO $ putStr (show p) >> putStr " ->" >> putStrLn msg
+
+
+
+
+
+--call host port proc params= do
+--   port <- getPort
+--   listen port <|> return
+--   parms <- logged $ return params
+--   callTo host port proc parms
+--   close
+--
+--distribute proc= do
+--   case dataFor proc
+--    Nothing -> proc
+--    Just dataproc -> do
+--      (h,p) <- bestNode dataproc
+--      callTo h p proc
+--
+--bestNode dataproc=
+--   nodes <- getNodes
+--      (h,p) <- bestMatch dataproc nodes   <- user defined
+--
+--bestMatch (DataProc nodesAccesed cpuLoad resourcesNeeded)  nodes= do
+--   nodesAccesed: node, response
+--
+--bestMove= do
+--   thisproc <- gets myProc
+--   case dataFor thisproc
+--      Nothing -> return ()
+--      Just dataproc -> do
+--        (h,p) <- bestNode dataproc
+--        moveTo h p
+--
+--
+--inNetwork= do
+--   p <- getPort
+--   listen p <|> return ()
+
+ src/Transient/Backtrack.hs view
@@ -0,0 +1,81 @@+{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE ExistentialQuantification #-}
+
+-- | <https://www.fpcomplete.com/user/agocorona/the-hardworking-programmer-ii-practical-backtracking-to-undo-actions>
+
+module Transient.Backtrack (registerUndo, onUndo, undo, retry, undoCut) where
+
+import Transient.Base
+import Data.Typeable
+import Control.Applicative
+import Control.Monad.State
+import Unsafe.Coerce
+import System.Mem.StableName
+
+data Backtrack= forall a b.Backtrack{backtracking :: Bool
+                                    ,backStack :: [EventF]}
+                                    deriving Typeable
+
+-- | assures that backtracking will not go further back
+undoCut :: TransientIO ()
+undoCut= Transient $ do
+     delSessionData $ Backtrack False []
+     return $ Just ()
+
+-- | the secod parameter will be executed when backtracking
+{-# NOINLINE onUndo #-}
+onUndo :: TransientIO a -> TransientIO a -> TransientIO a
+onUndo ac bac= do
+   r<-registerUndo $ Transient $ do
+     Backtrack back _ <- getSessionData `onNothing` return (Backtrack False [])
+     runTrans $ if back then bac  else ac
+   return r
+
+-- | register an action that will be executed when backtracking
+{-# NOINLINE registerUndo #-}
+registerUndo :: TransientIO a -> TransientIO a
+registerUndo f  = Transient $ do
+   cont@(EventF x _ _ _ _ _ _ _ _)  <- get   !> "backregister"
+   md  <- getSessionData
+   ss <- case md of
+        Just (bss@(Backtrack b (bs@((EventF x'  _ _ _ _ _ _ _ _):_)))) -> do
+            addrx  <- addr x
+            addrx' <- addr x'         -- to avoid duplicate backtracking points
+            return $ if addrx == addrx' then bss else  Backtrack b $ cont:bs
+        Nothing ->  return $ Backtrack False [cont]
+   setSessionData ss
+   runTrans f
+   where
+   addr x = liftIO $ return . hashStableName =<< (makeStableName $! x)
+
+-- | restart the flow forward from this point on
+retry :: TransientIO ()
+retry= do
+    Backtrack _ stack <- getSessionData `onNothing` return (Backtrack False [])
+    setSData $ Backtrack False stack
+
+-- | execute backtracking. It execute the registered actions in reverse order.
+--
+-- If the backtracking flag is changed the flow proceed  forward from that point on.
+--
+--If the backtrack stack is finished or undoCut executed, `undo` will stop.
+undo :: TransientIO a
+undo= Transient $ do
+  bs <- getSessionData  `onNothing` return nullBack            !>"GOBACK"
+  goBackt  bs
+
+  where
+  nullBack= Backtrack False []
+  goBackt (Backtrack _ [])= return Nothing                     !> "END"
+  goBackt (Backtrack b (stack@(first@(EventF x fs _ _  _ _ _ _ _): bs)))= do
+--        put first{replay=True}
+        setSData $ Backtrack True stack
+        mr <-  runClosure first                                !> "RUNCLOSURE"
+        Backtrack back _ <- getSessionData `onNothing` return nullBack
+                                                               !>"END RUNCLOSURE"
+        case back of
+           True ->  goBackt $ Backtrack True bs                !> "BACK AGAIN"
+           False -> case mr of
+                   Nothing -> return empty                     !> "FORWARD END"
+                   Just x ->  runContinuation first x          !> "FORWARD EXEC"
+
+ src/Transient/Base.hs view
@@ -0,0 +1,683 @@+{-# LANGUAGE ScopedTypeVariables #-}
+-----------------------------------------------------------------------------
+--
+-- Module      :  Base
+-- Copyright   :
+-- License     :  GPL (Just (Version {versionBranch = [3], versionTags = []}))
+--
+-- Maintainer  :  agocorona@gmail.com
+-- Stability   :
+-- Portability :
+--
+-- | See http://github.com/agocorona/transient
+-- everithing in this module is exported in order to allow extensibility.
+-----------------------------------------------------------------------------
+{-# LANGUAGE ExistentialQuantification #-}
+{-# LANGUAGE FlexibleContexts          #-}
+{-# LANGUAGE FlexibleInstances         #-}
+{-# LANGUAGE MultiParamTypeClasses     #-}
+{-# LANGUAGE DeriveDataTypeable        #-}
+-- show
+module Transient.Base  where
+-- /show
+
+import           Control.Applicative
+import           Control.Monad.State
+import           Data.Dynamic
+import qualified Data.Map               as M
+import           Data.Monoid
+import           Debug.Trace
+import           System.IO.Unsafe
+import           Unsafe.Coerce
+import           Control.Exception
+import           Control.Concurrent
+import           Control.Concurrent.STM
+import           System.Mem.StableName
+import           Data.Maybe
+import           GHC.Conc
+import           Data.List
+import           Data.IORef
+
+
+{-# INLINE (!>) #-}
+(!>) =  const . id -- flip trace
+infixr 0 !>
+
+data TransIO  x = Transient  {runTrans :: StateT EventF IO (Maybe x)}
+type SData= ()
+
+type EventId= Int
+
+type TransientIO= TransIO
+
+data EventF  = forall a b . EventF{xcomp       :: TransientIO a
+                                  ,fcomp       :: [b -> TransientIO b]
+                                  ,mfData      :: M.Map TypeRep SData
+                                  ,mfSequence  :: Int
+                                  ,threadId    :: ThreadId
+                                  ,freeTh      :: Bool
+                                  ,parent      :: Maybe EventF
+                                  ,children    :: TVar[EventF]
+                                  ,maxThread   :: Maybe (P Int)
+                                  }
+                                  deriving Typeable
+
+type P= IORef
+newp= newIORef
+
+
+--(=:) :: P a  -> (a -> a) -> IO()
+(=:) n f= liftIO $ atomicModifyIORef' n $  \v ->  ((f v),())
+
+addr x= show $ unsafePerformIO $ do
+       st <- makeStableName $! x
+       return $ hashStableName st
+
+
+
+
+instance MonadState EventF  TransientIO where
+  get=  Transient $ get >>= return . Just
+  put x= Transient $ put x >> return (Just ())
+
+type StateIO= StateT EventF  IO
+
+--type TransientIO= Transient StateIO
+
+--runTrans ::  TransientIO x -> StateT EventF  IO (Maybe x)
+--runTrans (Transient mx) = mx
+
+
+runTransient :: TransientIO x -> IO (Maybe x, EventF)
+runTransient t= do
+
+  th <- myThreadId
+  let eventf0=  EventF  empty [] M.empty 0
+          th False  Nothing  (unsafePerformIO $ newTVarIO []) Nothing
+
+
+  runStateT (runTrans t) eventf0{threadId=th} !> "MAIN="++show th
+
+
+
+
+-- | get the continuation context: closure, continuation, state, child threads etc
+getCont ::(MonadState EventF  m) => m EventF
+getCont = get
+
+-- | run the continuation context
+runCont :: EventF -> StateIO ()
+runCont (EventF  x fs _ _  _ _  _ _ _)= runTrans ((unsafeCoerce x') >>= compose ( fs)) >> return ()
+    where
+    x'=  do
+--           modify $ \s -> s{replay=True}
+           r<- x
+--           modify $ \s -> s{replay=False}
+           return r
+
+{-
+runCont cont= do
+     mr <- runClosure cont
+     case mr of
+         Nothing -> return Nothing
+         Just r -> runContinuation cont r
+-}
+
+-- | compose a list of continuations
+compose []= const empty
+compose (f: fs)= \x -> f x >>= compose fs
+
+
+-- | run the closure  (the 'x'  in 'x >>= f') of the current bind operation.
+runClosure :: EventF -> StateIO (Maybe a)
+runClosure (EventF x _ _ _ _ _ _ _ _) =  unsafeCoerce $ runTrans x
+
+-- | run the continuation (the 'f' in 'x >> f') of the current bind operation
+runContinuation ::  EventF -> a -> StateIO (Maybe b)
+runContinuation (EventF _ fs _ _ _ _  _ _ _) x= runTrans $  (unsafeCoerce $ compose $  fs) x
+
+instance   Functor TransientIO where
+  fmap f mx=   -- Transient $ fmap (fmap f) $ runTrans mx
+    do
+     x <- mx
+     return $ f x
+
+instance Applicative TransientIO where
+  pure a  = Transient . return $ Just a
+
+
+  f <*> g = Transient $ do
+
+         rf <- liftIO $ newIORef Nothing
+         rg <- liftIO $ newIORef Nothing   -- !> "NEWIOREF"
+
+         cont@(EventF _ fs a b c d peers children g1) <- get   -- !> "APLICATIVE DOIT"
+
+         let
+             appg x = Transient $  do
+                   liftIO $ writeIORef rg $ Just x :: StateIO ()
+                   k <- liftIO $ readIORef rf
+                   return $ k <*> Just x  -- !> "RETURNED: " ++ show(isJust k)++ show(isJust x)
+
+
+             appf k = Transient $  do
+                   liftIO $ writeIORef rf  $ Just k :: StateIO ()
+                   x<- liftIO $ readIORef rg
+                   return $ Just k <*> x  --  !> "RETURNED: " ++ show(isJust k)++ show(isJust x)
+
+
+
+         put $ EventF f (unsafeCoerce appf:  fs)
+                                          a b c d peers children g1
+         k <- runTrans f
+         was <- getSessionData `onNothing` return NoRemote
+         if was== WasRemote
+           then  return Nothing
+           else do
+             liftIO $ writeIORef rf  k -- :: StateIO ()
+
+             mfdata <- gets mfData
+             put $ EventF g (unsafeCoerce appg :  fs) mfdata b c d peers  children g1
+
+
+             x <- runTrans g              !> "RUN g"
+             liftIO $ writeIORef rg  x
+             return $ k <*> x
+
+-- | dynamic serializable data for logging
+data IDynamic= IDyns String | forall a.(Read a, Show a,Typeable a) => IDynamic a
+
+instance Show IDynamic where
+  show (IDynamic x)= show $ show x
+  show (IDyns s)= show s
+
+instance Read IDynamic where
+  readsPrec n str= map (\(x,s) -> (IDyns x,s)) $ readsPrec n str
+
+
+type Recover= Bool
+type CurrentPointer= [LogElem]
+type LogEntries= [LogElem]
+data LogElem=  WaitRemote | Exec | Step IDynamic deriving (Read,Show)
+data Log= Log Recover  CurrentPointer LogEntries deriving Typeable
+
+
+instance  Alternative TransientIO where
+  empty = Transient $ return  Nothing
+  (<|>) = mplus
+
+--  Transient f <|> Transient g= Transient $ do
+--         k <-   f
+--         x <-   g
+--         return $ k <|> x
+
+data RemoteStatus=  WasRemote | NoRemote deriving (Typeable, Eq)
+
+instance MonadPlus TransientIO where
+    mzero= empty
+    mplus  x y=  Transient $ do
+         mx <- runTrans x    -- !> "RUNTRANS11111"
+         was <- getSessionData `onNothing` return NoRemote
+         if was== WasRemote
+           then return Nothing
+           else case mx of
+             Nothing -> runTrans y   --  !> "RUNTRANS22222"
+             justx -> return justx
+
+-- | a sinonym of empty that can be used in a monadic expression. it stop the
+-- computation
+stop :: TransientIO a
+stop= Control.Applicative.empty
+
+instance Monoid a => Monoid (TransientIO a) where
+  mappend x y = mappend <$> x <*> y
+  mempty= return mempty
+
+-- | set the current closure and continuation for the current statement
+setEventCont ::   TransientIO a -> (a -> TransientIO b) -> StateIO ()
+setEventCont x f  = do
+   st@(EventF   _ fs d n  r applic  ch rc bs)  <- get
+   put $ EventF x ( unsafeCoerce f : fs) d n  r applic  ch rc bs
+
+
+-- | reset the closure and continuation. remove inner binds than the prevous computations may have stacked
+-- in the list of continuations.
+resetEventCont :: Maybe a -> StateIO ()
+resetEventCont mx =do
+   st@(EventF _ fs d n  r nr  ch rc bs)  <- get
+
+   let f= \mx ->  case mx of
+                       Nothing -> empty
+                       Just x  -> (unsafeCoerce $ head fs)  x
+   put $ EventF  (f mx) ( tailsafe fs)d n  r nr  ch rc bs
+   where
+   tailsafe []=[]
+   tailsafe (x:xs)= xs
+
+
+instance Monad TransientIO where
+      return x = Transient $ return $ Just x
+      x >>= f  = Transient $ do
+        setEventCont x  f
+
+        mk <- runTrans x
+        resetEventCont mk
+        case mk of
+           Just k  -> do
+               runTrans $ f k
+
+           Nothing -> return Nothing
+
+
+
+
+--instance MonadTrans (Transient ) where
+--  lift mx = Transient $ mx >>= return . Just
+
+instance MonadIO TransientIO where
+  liftIO x = Transient $ liftIO x >>= return . Just --     let x= liftIO io in x `seq` lift x
+
+
+
+
+-- * Threads
+
+waitQSemB sem= atomicModifyIORef' sem $ \n -> if n > 0 then(n-1,True) else (n,False)
+signalQSemB sem= atomicModifyIORef' sem  $ \n ->  (n + 1,())
+
+-- | set the maximun number of threads for a procedure. It is useful for the
+threads :: Int -> TransientIO a -> TransientIO a
+threads n proc= Transient $ do
+   msem <- gets maxThread
+   sem <- liftIO $ newIORef n
+   modify $ \s -> s{maxThread= Just sem}
+   r <- runTrans proc
+   modify $ \s -> s{maxThread = msem} -- restore it
+   return r
+-- | delete all the previous childs generated by the expressions and continue execution
+-- of the current thread.
+oneThread :: TransientIO a -> TransientIO a
+oneThread comp=  do
+   chs <- liftIO $ newTVarIO []
+   r <- comp
+   modify $ \ s -> s{children= chs}
+   killChilds
+   return r
+
+
+
+-- | The threads generated in the process passed as parameter will not be killed.
+freeThreads :: TransientIO a -> TransientIO a
+freeThreads proc= Transient $ do
+     st <- get
+     put st{freeTh= True}
+     r <- runTrans proc
+     modify $ \st -> st{freeTh= freeTh st}
+     return r
+
+-- | The threads will be killed when the parent thread dies. That is the default
+-- This can be invoked to revert the effect of `freeThreads`
+hookedThreads :: TransientIO a -> TransientIO a
+hookedThreads proc= Transient $ do
+     st <- get
+     put st{freeTh= False}
+     r <- runTrans proc
+     modify $ \st -> st{freeTh= freeTh st}
+     return r
+
+
+-- | kill all the child processes
+killChilds :: TransientIO()
+killChilds= Transient $  do
+   cont <- get
+   liftIO $  killChildren cont
+   return $ Just ()
+
+-- * extensible state: session data management
+
+-- | Get the session data for the desired type if there is any.
+getSessionData ::  (MonadState EventF m,Typeable a) =>  m (Maybe a)
+getSessionData =  resp where
+ resp= gets mfData >>= \list  ->
+    case M.lookup ( typeOf $ typeResp resp ) list  of
+      Just x  -> return . Just $ unsafeCoerce x
+      Nothing -> return $ Nothing
+ typeResp :: m (Maybe x) -> x
+ typeResp= undefined
+
+-- | getSessionData specialized for the Transient monad. if Nothing, the
+-- monadic computation does not continue.
+--
+-- If there is no such data, `getSData`  silently stop the computation.
+-- That may or may not be the desired behaviour.
+-- To make sure that this does not get unnoticed, use this construction:
+--
+-- >  getSData <|> error "no data"
+--
+getSData ::  Typeable a => TransIO  a
+getSData= Transient getSessionData
+
+
+-- | set session data for this type. retrieved with getSessionData orr getSData
+setSessionData ::  (MonadState EventF m, Typeable a) => a -> m ()
+setSessionData  x= do
+  let t= typeOf x in  modify $ \st -> st{mfData= M.insert  t (unsafeCoerce x) (mfData st)}
+
+-- | a shorter name for setSessionData
+setSData ::  ( MonadState EventF m,Typeable a) => a -> m ()
+setSData= setSessionData
+
+delSessionData x=
+  modify $ \st -> st{mfData= M.delete (typeOf x ) (mfData st)}
+
+delSData :: ( MonadState EventF m,Typeable a) => a -> m ()
+delSData= delSessionData
+
+--withSData ::  ( MonadState EventF m,Typeable a) => (Maybe a -> a) -> m ()
+--withSData f= modify $ \st -> st{mfData=
+--    let dat = mfData st
+--        mx= M.lookup typeofx dat
+--        mx'= case mx of Nothing -> Nothing; Just x -> unsafeCoerce x
+--        fx=  f mx'
+--        typeofx= typeOf $ typeoff f
+--    in  M.insert typeofx  (unsafeCoerce fx) dat}
+--    where
+--    typeoff :: (Maybe a -> a) -> a
+--    typeoff = undefined
+----
+
+-- | generator of identifiers
+genNewId :: MonadIO m => MonadState EventF m =>  m Int
+genNewId=  do
+          st <- get
+
+          let n= mfSequence st
+          put $ st{mfSequence= n+1}
+          return n
+
+refSequence :: IORef Int
+refSequence= unsafePerformIO $ newp 0
+
+
+
+data Loop= Once | Loop | Multithread deriving Eq
+
+-- | variant of `parallel` that repeatedly executes the IO computation and kill the previously created childs
+waitEvents ::   IO b -> TransientIO b
+waitEvents io= do
+   r <- parallel (Right <$> io)
+   killChilds
+   return r
+
+-- | variant of + parallel` that execute the IO computation once, and kill the previous child threads
+async  ::  IO b -> TransientIO b
+async io= do
+   r <- parallel  (Left <$>io)
+   killChilds
+   return r
+
+spawn ::  IO b -> TransientIO b
+spawn io= freeThreads $ do
+   r <- parallel (Right <$>io)
+   return r
+
+data EventValue= EventValue SData deriving Typeable
+
+-- |  return empty to the current thread and launch the IO action in a new thread and attaches the continuation after it.
+-- if the result of the action is `Right` the process is repeated. if not, it finish.
+--
+-- If the maximum number of threads, set with `threads` has been reached  `parallel` perform
+-- the work sequentially, in the current thread.
+--
+-- when finish, increase the counter of threads available, if there is a limitation of them.
+
+parallel  ::    IO (Either b b) -> TransientIO b
+parallel  ioaction= Transient$   do
+    cont <- getCont                    -- !> "PARALLEL"
+    mv <- getSessionData
+    case mv  of
+     Just (EventValue v)  -> do
+        delSessionData $ EventValue () -- !> "ISJUST "
+        return  $ Just $ unsafeCoerce v
+     Nothing -> do
+        liftIO  $ loop cont    ioaction
+        return Nothing
+
+
+
+
+loop (cont'@(EventF x fs a b c d peers childs g))  rec  =  do
+  chs <- liftIO $ newTVarIO []
+  let cont = EventF x fs a b c d (Just cont') chs g
+      iocont dat=
+          runStateT ( do
+             setSessionData . EventValue $ unsafeCoerce dat
+             runCont cont
+             ) cont
+             >> return ()
+      loop'= do
+        mdat <- rec
+        case mdat of
+         Left dat -> iocont dat
+
+         Right dat -> do
+              forkMaybe cont $ iocont dat
+              loop'
+
+  forkMaybe  cont loop'
+  where
+      forkMaybe cont proc = do
+         dofork <- case maxThread cont of
+                  Nothing -> return True
+                  Just sem -> do
+                    dofork <- waitQSemB sem
+                    if dofork then  return True else return False
+
+         if dofork
+            then  do
+                 th <- forkFinally proc $ \me -> do
+                         case me of -- !> "THREAD ENDED" of
+                          Left  e -> do
+                           when (fromException e /= Just ThreadKilled)$ liftIO $ print e
+                           killChildren  cont  !> "KILL RECEIVED" ++ (show $ unsafePerformIO myThreadId)
+
+                          Right _ -> do
+                             --  if parent is alive
+                             --  then remove himself from the list (with free)
+                             --  and pass his active children to his parent
+                             return ()
+                             th <- myThreadId
+                             mparent <- free th cont
+                             case mparent of
+                              Nothing  ->  return()
+                              Just parent -> atomically $ do
+                                     chs' <- readTVar $ children cont
+                                     chs  <- (readTVar $ children parent)
+                                     writeTVar (children parent)$ chs ++ chs'
+                                     return ()
+
+                         case maxThread cont of
+                           Just sem -> signalQSemB sem
+                           Nothing -> return ()
+
+
+                 addThread cont' cont{threadId=th}  -- !>  "thread created: "++ show th
+
+            else proc  -- !> "NO THREAD"
+
+
+
+free th env= do
+  if isNothing $ parent env
+   then  return Nothing  !>  show th ++ " orphan"
+   else do
+    let msibling= fmap children $ parent env
+
+    case msibling of
+     Nothing -> return Nothing
+     Just sibling  -> do
+       found <- atomically $ do
+                sbs <- readTVar sibling
+                let (sbs', found) = drop [] th  sbs -- !> "search "++show th ++ " in " ++ show (map threadId sbs)
+                when found $ writeTVar sibling sbs'
+                return found
+       if (not found && isJust (parent env))
+         then free th $ fromJust $ parent env -- !> "toparent"
+         else return $ Just env
+
+   where
+   drop processed th []= (processed,False)
+   drop processed th (ev:evts)| th == threadId ev= (processed ++ evts, True)
+                    | otherwise= drop (ev:processed) th evts
+
+
+addThread parent child = when(not $ freeTh parent) $ do
+   let headpths= children parent
+   atomically $ do
+       ths <- readTVar headpths
+       writeTVar headpths $  child:ths
+
+-- | kill all the threads associated with the continuation context
+killChildren  cont = do
+     forkIO $ do
+        let childs= children cont   !> "killChildren list= "++ addr (children cont)
+        ths <- atomically $ do
+           ths <- readTVar childs
+           writeTVar childs []
+           return ths
+        mapM_ (killThread . threadId) ths  !> "KILLEVENT " ++ show (map threadId ths)
+     return ()
+
+
+type EventSetter eventdata response= (eventdata ->  IO response) -> IO ()
+type ToReturn  response=  IO response
+
+-- | deinvert an event handler. The first parameter is the event handler to be deinverted
+-- the second is the value to return to the event handler
+-- it configures the event handler by calling the first parameter, that set the event
+-- handler, with the current continuation
+react
+  :: Typeable eventdata
+  => EventSetter eventdata response
+  -> ToReturn  response
+  -> TransientIO eventdata
+react setHandler iob= Transient $ do
+        cont    <- getCont
+        mEvData <- getSessionData
+        case mEvData of
+          Nothing -> do
+            liftIO $ setHandler $ \dat ->do
+--              let cont'= cont{mfData = M.insert (typeOf dat)(unsafeCoerce dat) (mfData cont)}
+              runStateT (setSData dat >> runCont cont) cont
+              iob
+            return Nothing
+          Just dat -> delSessionData dat >> return (Just  dat)
+
+
+-- * non-blocking keyboard input
+
+getLineRef= unsafePerformIO $ newTVarIO Nothing
+
+
+roption= unsafePerformIO $ newMVar []
+
+-- | install a event receiver that wait for a string and trigger the continuation when this string arrives.
+option :: (Typeable b, Show b, Read b, Eq b) =>
+     b -> [Char] -> TransientIO b
+option ret message= do
+    let sret= show ret
+
+    liftIO $ putStrLn $ "Enter  "++sret++"\tto: " ++ message
+    liftIO $ modifyMVar_ roption $ \msgs-> return $ sret:msgs
+    waitEvents  $ getLine' (==ret)
+    liftIO $ putStrLn $ show ret ++ " chosen"
+    return ret
+
+
+-- | validates an input entered in the keyboard in non blocking mode. non blocking means that
+-- the user can enter also anything else to activate other option
+-- unlike `option`, input only wait for one valid response
+input :: (Typeable a, Read a) => (a -> Bool) -> TransientIO a
+input cond= Transient . liftIO . atomically $ do
+       mr <- readTVar getLineRef
+       case mr of
+         Nothing -> retry
+         Just r ->
+            case reads1 r  of
+            (s,_):_ -> if cond s  --  !> show (cond s)
+                     then do
+                       writeTVar  getLineRef Nothing -- !>"match"
+                       return $ Just s
+
+                     else return Nothing
+            _ -> return Nothing
+
+-- | non blocking `getLine` with a validator
+getLine' cond=    do
+     atomically $ do
+       mr <- readTVar getLineRef
+       case mr of
+         Nothing -> retry
+         Just r ->
+            case reads1 r of --  !> ("received " ++  show r ++ show (unsafePerformIO myThreadId)) of
+            (s,_):_ -> if cond s -- !> show (cond s)
+                     then do
+                       writeTVar  getLineRef Nothing -- !>"match"
+                       return s
+
+                     else retry
+            _ -> retry
+
+reads1 s=x where
+      x= if typeOf(typeOfr x) == typeOf "" then unsafeCoerce[(s,"")] else readsPrec 0 s
+      typeOfr :: [(a,String)] ->  a
+      typeOfr  = undefined
+
+inputLoop=  do
+    putStrLn "Press end to exit"
+    inputLoop'  -- !> "started inputLoop"
+    where
+
+    inputLoop'= do
+           r<- getLine
+           if r=="end" then putMVar rexit () else do
+              let rs = breakSlash [] r
+              mapM_ (\ r -> do threadDelay 1000
+                               atomically . writeTVar  getLineRef $ Just r) rs
+              inputLoop'
+
+    breakSlash :: [String] -> String -> [String]
+    breakSlash s ""= s
+    breakSlash res s=
+      let (r,rest) = span(/= '/') s
+      in breakSlash (res++[r]) $ tail1 rest
+      where
+      tail1 []=[]
+      tail1 x= tail x
+
+
+rexit= unsafePerformIO newEmptyMVar
+
+stay=  takeMVar rexit
+
+-- | keep the main thread running, initiate the asynchronous keyboard input and execute
+-- the transient computation.
+keep mx = do
+   forkIO $ inputLoop
+   forkIO $ runTransient mx  >> return ()
+   stay
+
+-- | force the finalization of the main thread and thus, all the application
+exit :: TransientIO a
+exit= do
+  liftIO $ putStrLn "Tempus fugit: exit"
+  liftIO $ putMVar rexit   True
+  return undefined
+
+-- | alternative operator for maybe values. Used  in infix mode
+onNothing :: Monad m => m (Maybe b) -> m b -> m b
+onNothing iox iox'= do
+       mx <- iox
+       case mx of
+           Just x -> return x
+           Nothing -> iox'
+ src/Transient/Indeterminism.hs view
@@ -0,0 +1,101 @@+-----------------------------------------------------------------------------
+--
+-- Module      :  Transient.Indeterminism
+-- Copyright   :
+-- License     :  GPL (Just (Version {versionBranch = [3], versionTags = []}))
+--
+-- Maintainer  :  agocorona@gmail.com
+-- Stability   :
+-- Portability :
+--
+-- | see <https://www.fpcomplete.com/user/agocorona/beautiful-parallel-non-determinism-transient-effects-iii>
+--
+-----------------------------------------------------------------------------
+{-# LANGUAGE BangPatterns #-}
+module Transient.Indeterminism (
+choose, choose', collect, group --, found
+) where
+
+import Transient.Base
+import Control.Monad.IO.Class
+import Data.IORef
+import Control.Applicative
+import Data.Monoid
+import Control.Concurrent
+import Data.Typeable
+import Control.Monad.State
+import Control.Concurrent.STM as STM
+import GHC.Conc
+
+
+-- | slurp a list of values and process them in parallel . To limit the number of processing
+-- threads, use `threads`
+choose  ::  [a] -> TransientIO a
+choose []= empty
+choose   xs = do
+    evs <- liftIO  $ newIORef xs
+    parallel   $ do
+           es <- atomicModifyIORef' evs $ \es -> let !tes= tail es in (tes,es)
+           case es of
+            [x]  -> return $ Left $ head es
+            x:_  -> return $ Right x
+
+-- | group the output of a possible multithreaded process in groups of n elements.
+group :: Int -> TransientIO a -> TransientIO [a]
+group num proc =  do
+    v <- liftIO $ newIORef (0,[])
+    x <- proc
+    n <- liftIO $ atomicModifyIORef' v $ \(n,xs) -> let !n'=n +1 in ((n', x:xs),n')
+    if n < num
+      then stop
+      else liftIO $ atomicModifyIORef v $ \(n,xs) ->  ((0,[]),xs)
+
+-- | alternative definition with more parallelism
+choose' :: [a] -> TransientIO a
+choose'  xs = foldl (<|>) empty $ map (parallel . return . Left) xs
+
+
+--newtype Collect a= Collect (MVar (Int, [a])) deriving Typeable
+
+-- collect the results of a search done in parallel, usually initiated by
+-- `choose` . The results are added to the collection with `found`
+--
+--
+
+
+-- | execute a process and get the first n solutions.
+-- if the process end without finding the number of solutions requested, it return the fond ones
+-- if he find the number of solutions requested, it kill the threads of the process and return
+-- It works monitoring the solutions found and the number of active threads.
+-- If the first parameter is 0, collect will return all the results
+collect ::  Int -> TransientIO a -> TransientIO [a]
+collect n search=  do
+  rv <- liftIO $ atomically $ newTVar (0,[]) !> "NEWMVAR"
+  endflag <- liftIO $ newTVarIO False
+  st <- get
+  let any1 = do
+        r <- search   !> "ANY"
+        liftIO $ atomically $ do
+            (n1,rs) <- readTVar rv
+            writeTVar  rv (n1+1,r:rs) !> "MODIFY"
+        stop
+
+      detect= freeThreads $ do
+          xs <- async $ do
+             threadDelay 1000 -- to allow some activity before monitoring it
+             atomically $ do
+                (n',xs) <- readTVar rv
+                ns <- readTVar $ children st
+
+                if (n > 0 && n' >= n) ||  null ns  !> show (n,n') !> (show $ length ns)
+                  then return xs
+                  else retry
+
+          th <- liftIO $ myThreadId !> "KILL"
+          stnow <- get
+          liftIO $ killChildren st
+          liftIO $ addThread st stnow
+          return  xs
+
+  (any1 >> stop)  <|> detect
+
+ src/Transient/Logged.hs view
@@ -0,0 +1,90 @@+-----------------------------------------------------------------------------
+--
+-- Module      :  Transient.Logged
+-- Copyright   :
+-- License     :  GPL-3
+--
+-- Maintainer  :  agocorona@gmail.com
+-- Stability   :
+-- Portability :
+--
+-- |
+--
+-----------------------------------------------------------------------------
+{-# LANGUAGE  ExistentialQuantification #-}
+module Transient.Logged  where
+
+import Data.Typeable
+import Unsafe.Coerce
+import Transient.Base
+import Control.Applicative
+import Control.Monad.IO.Class
+
+--data IDynamic= IDyns String | forall a.(Read a, Show a,Typeable a) => IDynamic a
+
+--instance Show IDynamic where
+--  show (IDynamic x)= show $ show x
+--  show (IDyns s)= show s
+--
+--instance Read IDynamic where
+--  readsPrec n str= map (\(x,s) -> (IDyns x,s)) $ readsPrec n str
+
+
+fromIDyn :: (Read a, Show a, Typeable a) => IDynamic -> a
+fromIDyn (IDynamic x)= unsafeCoerce x
+
+fromIDyn (IDyns s)=r where r= read s !> "read " ++ s ++ "to type "++ show (typeOf r)
+
+toIDyn x= IDynamic x
+
+-- | synonymous of `step`
+logged :: (Show a, Read a, Typeable a) => TransientIO a -> TransientIO a
+logged= step
+
+
+
+-- | write the result of the computation in the log and return it.
+-- but if there is data in the internal log, it read the data from the log and
+-- do not execute the computation.
+--
+-- It accept nested step's. The effect is that if the outer step is executed completely
+-- the log of the inner steps are erased. If it is not the case, the inner steps are logged
+-- this reduce the log of large computations to the minimum. That is a feature not present
+-- in the package Workflow.
+--
+-- >  r <- step $ do
+-- >          step this :: TransIO ()
+-- >          step that :: TransIO ()
+-- >          step thatOther
+-- >  liftIO $ print r
+--
+--  when `print` is executed, the log is just the value of r.
+--
+--  but when `thatOther` is executed the log is: [Exec,(), ()]
+--
+step :: (Show a, Read a, Typeable a) => TransientIO a -> TransientIO a
+step mx=  do
+    Log recover rs full <- getSData <|> return ( Log False  [][])
+
+    case (recover,rs) of
+      (True, Step x: rs') -> do
+            setSData $ Log recover rs' full
+            return $ fromIDyn x  !>  "read in step:" ++ show x
+
+      (True,Exec:rs') -> do
+            setSData $ Log recover rs' full
+            mx
+
+      (True, WaitRemote:rs') -> do
+            setSData (Log recover rs' full) !> "waitRemote2"
+            empty
+
+      _ -> do
+            let add= Exec:  full
+            setSData $ Log False add add
+            r <-  mx
+            let add= Step (toIDyn r): full
+            setSData $ Log False add add
+            return  r
+
+
+ src/Transient/Move.hs view
@@ -0,0 +1,231 @@+-----------------------------------------------------------------------------
+--
+-- Module      :  Transient.Move
+-- Copyright   :
+-- License     :  GPL-3
+--
+-- Maintainer  :  agocorona@gmail.com
+-- Stability   :
+-- Portability :
+--
+-- | see <https://www.fpcomplete.com/user/agocorona/moving-haskell-processes-between-nodes-transient-effects-iv>
+-----------------------------------------------------------------------------
+{-# LANGUAGE DeriveDataTypeable , ExistentialQuantification
+    ,ScopedTypeVariables, StandaloneDeriving #-}
+module Transient.Move where
+import Transient.Base
+import Transient.Logged
+import Data.Typeable
+import Control.Applicative
+import Network
+import Network.HTTP
+import Control.Monad.IO.Class
+import System.IO
+import Control.Exception
+import Data.Maybe
+import Unsafe.Coerce
+import System.Process
+import System.Directory
+import Control.Monad
+import Network.Info
+import System.IO.Unsafe
+import Control.Concurrent.STM as STM
+import Data.Monoid
+import qualified Data.Map as M
+import Data.List (nub,(\\))
+
+
+
+-- | install in a remote node a haskell package with an executable transient service initialized with `listen`
+-- the package, the git repository and the main exectable must have the same name
+installService node port servport package= do
+  beamTo node port
+  liftIO $ do
+     let packagename= name package
+     exist <- doesDirectoryExist  packagename
+     when (not exist) $ do
+         runCommand $ "git clone "++ package
+         runCommand $ "cd "++ packagename
+         runCommand "cabal install"
+         createProcess $ shell $ "./dist/build/"++ packagename++"/"++packagename
+                                       ++ " " ++ show port
+         return()
+  where
+  name path=
+     let x= dropWhile (/= '/') path
+     in if x== "" then tail path else name $ tail    x
+
+-- | continue the execution in a new node
+-- all the previous actions from `listen` to this statement must have been logged
+beamTo :: HostName -> PortID -> TransientIO ()
+beamTo host port= do
+  Log rec log _ <- getSData <|> return (Log False [][])
+  if rec then return () else do
+      h <- liftIO $ connectTo host port
+      liftIO $ hSetBuffering h LineBuffering
+      liftIO $ hPutStrLn h (show $ reverse log) >> hFlush h
+      liftIO $ hClose h
+      delSData h
+      stop
+
+-- | execute in the remote node a process with the same execution state
+-- all the previous actions from `listen` to this statement must have been logged
+forkTo  :: HostName -> PortID -> TransientIO ()
+forkTo host port= do
+  Log rec log _<- getSData <|> return (Log False [][])
+  if rec then return () else do
+      h <- liftIO $ connectTo host port
+      liftIO $ hSetBuffering h LineBuffering
+      liftIO $ hPutStrLn h (show $ reverse log)  >> hFlush h
+      liftIO $ hClose h
+      delSData h
+
+-- | executes an action in another node.
+-- all the previous actions from `listen` to this statement must have been logged
+callTo :: (Show a, Read a,Typeable a) => HostName -> PortID -> TransIO a -> TransIO a
+callTo host port remoteProc= logged $ Transient $ do
+--      liftIO $ print "callto"
+      Log rec log fulLog <- getSessionData `onNothing` return (Log False [][])
+      if rec
+         then
+          runTrans $ do
+
+               Connection port  h sock <- getSData <|> error "callto: no hander"
+               r <- remoteProc !> "executing remoteProc" !> "CALLTO REMOTE" -- LOg="++ show fulLog
+               liftIO $ hPutStrLn h (show r) --  `catch` (\(e::SomeException) -> sClose sock)
+                -- !> "sent response, HANDLE="++ show h
+               setSData WasRemote
+               stop
+
+
+         else do
+
+            h <- liftIO $ connectTo host port
+            liftIO $ hPutStrLn h (show $ reverse fulLog) >> hFlush h !> "CALLTO LOCAL" -- send "++ show  log
+            let log'= WaitRemote:tail log
+            setSessionData $ Log rec log' log'
+            runTrans $ waitEvents $ do -- local side
+                   liftIO $ hSetBuffering h LineBuffering
+                   s <- hGetLine h
+--                   hClose h
+
+                   let r = read s
+
+                   return r   !> "read: " ++ s ++" response type= "++show( typeOf r)
+
+-- | A connectionless version of callTo for long running remote calls
+callTo' :: (Show a, Read a,Typeable a) => HostName -> PortID -> TransIO a -> TransIO a
+callTo' rhost rport remoteProc= logged $ do
+    (host,port) <- getMyNode
+    logged $ beamTo rhost rport
+    r <- logged remoteProc
+    logged $ beamTo host port
+    return r
+
+data Connection= Connection PortID Handle Socket deriving Typeable
+
+-- | Wait for messages and replay the rest of the monadic sequence with the log received.
+listen :: PortID ->  TransIO ()
+listen  port = do
+       setSData $ Log False [] []
+       sock <- liftIO $ withSocketsDo $ listenOn  port
+
+       (h,host,port1) <- parallel $ Right <$> accept sock
+                          `catch` (\(e::SomeException) -> sClose sock >> throw e)
+
+       liftIO $  hSetBuffering h LineBuffering  -- !> "LISTEN in "++ show (h,host,port1)
+
+       slog <- Transient $ liftIO $ (Just <$> hGetLine  h)
+                          `catch` (\(e::SomeException) -> print "ERR" >>  return Nothing)
+
+       setSData $ Connection port h sock  -- !> "setdata port=" ++ show port
+
+       let log= read slog   -- !> "read1 " ++ slog
+       setSData $ Log True log (reverse log)
+
+
+-- | init a Transient process in a interactive as well as in a replay mode.
+-- It is intended for twin processes that interact among them in different nodes.
+beamInit :: PortID -> TransIO a -> IO b
+beamInit port program=  keep $ do
+    listen port   <|> return ()
+    program
+
+
+
+
+instance Read PortNumber where
+  readsPrec n str= let [(n,s)]=   readsPrec n str in [(fromIntegral n,s)]
+
+
+deriving instance Read PortID
+deriving instance Typeable PortID
+
+-- * Level 2: connections node lists and operations with the node list
+
+data Node= Node{host :: HostName, port :: PortID, connection :: Maybe(Handle,Socket,HostName,PortID)} deriving (Eq,Typeable)
+
+instance Show Node where show (Node h p _)= show (h,p)
+instance Read Node where readsPrec _ s= let [((h,p),s')]= readsPrec 0 s in [((Node h p Nothing),s')]
+
+nodeList :: TVar  [Node]
+nodeList = unsafePerformIO $ newTVarIO []
+
+deriving instance Ord PortID
+
+myNode= unsafePerformIO $ atomically $ newTVar Nothing
+
+setMyNode h p= liftIO $ atomically $ writeTVar  myNode $ Just (h,p)
+getMyNode= Transient $ liftIO $ atomically $ readTVar myNode
+
+getNodes :: TransIO [Node]
+getNodes  = Transient $ Just <$> (liftIO $ atomically $ readTVar  nodeList)
+
+addNodes   nodes= Transient . liftIO . atomically $ do
+  prevnodes <- readTVar nodeList
+  writeTVar nodeList $ nub $ prevnodes ++  nodes
+  return $ Just ()
+
+--getInterfaces :: TransIO TransIO HostName
+--getInterfaces= do
+--   host <- logged $ do
+--      ifs <- liftIO $ getNetworkInterfaces
+--      liftIO $ mapM_ (\(i,n) ->putStrLn $ show i ++ "\t"++  show (ipv4 n) ++ "\t"++name n)$ zip [0..] ifs
+--      liftIO $ putStrLn "Select one: "
+--      ind <-  input ( < length ifs)
+--      return $ show . ipv4 $ ifs !! ind
+
+
+-- | execute a Transient action in each of the nodes connected. The results are aggregated with `mappend`
+clustered :: (Typeable a, Show a, Read a) => Monoid a => TransIO a -> TransIO a
+clustered proc= logged $ do
+     nodes <- step getNodes
+     logged $ foldr (<>) mempty $ map (\(Node h p _) -> callTo h p proc) nodes !> "fold"
+
+-- | a connectionless version of clustered for long running remote computations. Not tested
+clustered' proc= logged $ do
+     nodes <- step getNodes
+     logged $ mapM (\(Node h p _) -> callTo' h p proc) $ nodes
+
+-- | Connect to a new node to another. The other node will notify about this connection to
+-- all the nodes connected to him. the new connected node will receive the list of connected nodes
+-- the nodes will be updated with this list. it can be retrieved with `getNodes`
+connect ::   HostName ->  PortID ->  HostName ->  PortID -> TransientIO ()
+connect host  port   remotehost remoteport=  do
+    listen port <|> return ()
+    logged $ do
+        let n= Node host port Nothing
+        logged $ do
+             setMyNode host port
+             addNodes [n]
+             liftIO $ putStrLn $ "connecting to: "++ show (remotehost,remoteport)
+        newnode <- logged $ return n -- must pass my node the remote node or else it will use his own
+        port <- logged $ return port
+        nodes <- callTo remotehost remoteport   $ do
+                   clustered $  addNodes [newnode]
+                   getNodes
+
+        logged $ addNodes nodes
+        logged $ liftIO $ putStrLn $ "Connected to modes: " ++ show nodes
+
+
+ transient.cabal view
@@ -0,0 +1,53 @@+name: transient
+synopsis: A monad for extensible effects and primitives for unrestricted composability of applications
+homepage: http://www.fpcomplete.com/user/agocorona
+bug-reports: https://github.com/agocorona/transient/issues
+version: 0.1.0.0
+cabal-version: >=1.10
+build-type: Simple
+license: GPL-3
+license-file: LICENSE
+maintainer: agocorona@gmail.com
+category: Control
+author: Alberto G. Corona
+description:
+     see <http://github.com/agocorona/transient>
+
+data-dir: ""
+
+library
+    build-depends: base -any, mtl -any, random -any, containers -any,
+                   directory -any, filepath -any, stm -any, HTTP -any, network -any,
+                   transformers -any, process -any, network-info -any
+
+    exposed-modules: Transient.Indeterminism Transient.Base
+                     Transient.Backtrack Transient.Move Transient.Logged
+    exposed: True
+    buildable: True
+    default-language: Haskell2010
+    hs-source-dirs: src .
+    other-modules:
+
+executable transient
+    build-depends: base >4 && <5, mtl -any, random -any, containers -any,
+                   directory -any, filepath -any, stm -any, HTTP -any, network -any,
+                   transformers -any, transient -any
+    main-is: Main.hs
+    buildable: True
+    default-language: Haskell2010
+    hs-source-dirs: .
+    other-modules:
+
+executable move
+    build-depends: base -any, mtl -any, random -any, containers -any,
+                   directory -any, filepath -any, stm -any, HTTP -any, network -any,
+                   transformers -any, transient -any
+    main-is: move.hs
+    buildable: True
+    default-language: Haskell2010
+    hs-source-dirs: .
+    other-modules:
+
+source-repository head
+  type:     git
+  location: https://github.com/agocorona/transient