need help with monad transformers
Hello. I'm trying to add monad stack into network-conduit, and everything works except some details [1]. I've run runReaderT $ runTCPServer (wrapper around runResourceT) and inside conduit I want to run writer to gather results of inner computation. In inner computation I want to use IO, data from outter stack (ReaderT) so I'm running {-1-}: (k,t) <- lift $ runWriterT $ ask >>= \x -> tell [x] {- 1 -} and {-2-} (k,t) <- lift $ runWriterT $ do {- 2 -} x <- ask liftIO $ print $x+1 tell [x] and that will work (except I've thought I should not lift runWriterT, but calling functions inside. And finally in computation that will run once I want to register cleaning function (for example register $ putStrLn "cleaned") ({-3-}) (k,t) <- lift $ runWriterT $ do {- 3 -} x <- ask liftIO $ print $x+1 register $ print "freed2" tell [x] but I've got type error. If I'm running register outside runWriterT everything will work. I would apperated if there will be any suggestions how to make this code better or use register in internal computation (runWriterT) [1] https://gist.github.com/1941151 -- Best regards, Alexander V Vershilov
If I'm running register outside runWriterT everything will work.
Maybe just
lift $ register $ print "freed2"
or I didn't catch something?
2012/3/1 Alexander V Vershilov
Hello.
I'm trying to add monad stack into network-conduit, and everything works except some details [1].
I've run runReaderT $ runTCPServer (wrapper around runResourceT) and inside conduit I want to run writer to gather results of inner computation. In inner computation I want to use IO, data from outter stack (ReaderT) so I'm running {-1-}:
(k,t) <- lift $ runWriterT $ ask >>= \x -> tell [x] {- 1 -}
and {-2-}
(k,t) <- lift $ runWriterT $ do {- 2 -} x <- ask liftIO $ print $x+1 tell [x]
and that will work (except I've thought I should not lift runWriterT, but calling functions inside.
And finally in computation that will run once I want to register cleaning function (for example register $ putStrLn "cleaned") ({-3-})
(k,t) <- lift $ runWriterT $ do {- 3 -} x <- ask liftIO $ print $x+1 register $ print "freed2" tell [x]
but I've got type error. If I'm running register outside runWriterT everything will work.
I would apperated if there will be any suggestions how to make this code better or use register in internal computation (runWriterT)
[1] https://gist.github.com/1941151 -- Best regards, Alexander V Vershilov
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
It will not work due: gistfile1.hs:29:36: Could not deduce (m ~ ResourceT m0) from the context (Base m ~ IO, MonadReader SInit m, MonadIO m, IsSource src, Resource m) bound by the type signature for app :: (Base m ~ IO, MonadReader SInit m, MonadIO m, IsSource src, Resource m) => src m a1 -> Sink a1 m b -> ResourceT m b at gistfile1.hs:(29,1)-(59,27) `m' is a rigid type variable bound by the type signature for app :: (Base m ~ IO, MonadReader SInit m, MonadIO m, IsSource src, Resource m) => src m a1 -> Sink a1 m b -> ResourceT m b at gistfile1.hs:29:1 Expected type: Conduit a1 m a1 Actual type: Conduit a1 (ResourceT m0) a1 In the second argument of `(=$=)', namely `process2' In the second argument of `($=)', namely `(process1 =$= process2)' Thu, Mar 01, 2012 at 02:19:29PM +0400, Dmitry Olshansky wrote
If I'm running register outside runWriterT everything will work.
Maybe just
lift $ register $ print "freed2"
or I didn't catch something?
2012/3/1 Alexander V Vershilov
Hello.
I'm trying to add monad stack into network-conduit, and everything works except some details [1].
I've run runReaderT $ runTCPServer (wrapper around runResourceT) and inside conduit I want to run writer to gather results of inner computation. In inner computation I want to use IO, data from outter stack (ReaderT) so I'm running {-1-}:
(k,t) <- lift $ runWriterT $ ask >>= \x -> tell [x] {- 1 -}
and {-2-}
(k,t) <- lift $ runWriterT $ do {- 2 -} x <- ask liftIO $ print $x+1 tell [x]
and that will work (except I've thought I should not lift runWriterT, but calling functions inside.
And finally in computation that will run once I want to register cleaning function (for example register $ putStrLn "cleaned") ({-3-})
(k,t) <- lift $ runWriterT $ do {- 3 -} x <- ask liftIO $ print $x+1 register $ print "freed2" tell [x]
but I've got type error. If I'm running register outside runWriterT everything will work.
I would apperated if there will be any suggestions how to make this code better or use register in internal computation (runWriterT)
[1] https://gist.github.com/1941151 -- Best regards, Alexander V Vershilov
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
I've found a solution, I should not use lift for runWriterT, and should explicilty lift all computation of level I need, i.e. (lift.lift) for ask and lift for register. Thu, Mar 01, 2012 at 02:19:29PM +0400, Dmitry Olshansky wrote
If I'm running register outside runWriterT everything will work.
Maybe just
lift $ register $ print "freed2"
or I didn't catch something?
2012/3/1 Alexander V Vershilov
Hello.
I'm trying to add monad stack into network-conduit, and everything works except some details [1].
I've run runReaderT $ runTCPServer (wrapper around runResourceT) and inside conduit I want to run writer to gather results of inner computation. In inner computation I want to use IO, data from outter stack (ReaderT) so I'm running {-1-}:
(k,t) <- lift $ runWriterT $ ask >>= \x -> tell [x] {- 1 -}
and {-2-}
(k,t) <- lift $ runWriterT $ do {- 2 -} x <- ask liftIO $ print $x+1 tell [x]
and that will work (except I've thought I should not lift runWriterT, but calling functions inside.
And finally in computation that will run once I want to register cleaning function (for example register $ putStrLn "cleaned") ({-3-})
(k,t) <- lift $ runWriterT $ do {- 3 -} x <- ask liftIO $ print $x+1 register $ print "freed2" tell [x]
but I've got type error. If I'm running register outside runWriterT everything will work.
I would apperated if there will be any suggestions how to make this code better or use register in internal computation (runWriterT)
[1] https://gist.github.com/1941151 -- Best regards, Alexander V Vershilov
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Did you try to use transformers instead of mtl? I am just in doubt about it
in my work.
I've found that Conduit use it. So you remove extra dependency.
I hope that transformers have more readable messages (without FD) and you
can control what is "lift" more clear.
I have no experience although.
2012/3/2 Alexander V Vershilov
I've found a solution, I should not use lift for runWriterT, and should explicilty lift all computation of level I need, i.e. (lift.lift) for ask and lift for register.
Thu, Mar 01, 2012 at 02:19:29PM +0400, Dmitry Olshansky wrote
If I'm running register outside runWriterT everything will work.
Maybe just
lift $ register $ print "freed2"
or I didn't catch something?
2012/3/1 Alexander V Vershilov
Hello.
I'm trying to add monad stack into network-conduit, and everything works except some details [1].
I've run runReaderT $ runTCPServer (wrapper around runResourceT) and inside conduit I want to run writer to gather results of inner computation. In inner computation I want to use IO, data from outter stack (ReaderT) so I'm running {-1-}:
(k,t) <- lift $ runWriterT $ ask >>= \x -> tell [x] {- 1 -}
and {-2-}
(k,t) <- lift $ runWriterT $ do {- 2 -} x <- ask liftIO $ print $x+1 tell [x]
and that will work (except I've thought I should not lift runWriterT, but calling functions inside.
And finally in computation that will run once I want to register cleaning function (for example register $ putStrLn "cleaned") ({-3-})
(k,t) <- lift $ runWriterT $ do {- 3 -} x <- ask liftIO $ print $x+1 register $ print "freed2" tell [x]
but I've got type error. If I'm running register outside runWriterT everything will work.
I would apperated if there will be any suggestions how to make this code better or use register in internal computation (runWriterT)
[1] https://gist.github.com/1941151 -- Best regards, Alexander V Vershilov
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
participants (2)
-
Alexander V Vershilov -
Dmitry Olshansky