A while ago I asked similar question about hgearman client. With help I got in the List (https://mail.haskell.org/pipermail/beginners/2017-March/017435.html) and I implemented a gearman client in Haskell. (here the implementation http://stackoverflow.com/questions/42774191/how-does-hgearman-client-work) Unfortunately I need again some help be implementation of gearman worker. I post here only the snippet with the badly implemented code in hope to find again some help. (Complete implementation: http://stackoverflow.com/questions/43155857/how-does-hgearman-worker-work) Right gc -> do (res, _) <- flip S.runStateT gc $ do g <- (W.registerWorker name func) t <- W.runWorker gc (return ()) return t >> return () return res This throws exception: Couldn't match expected type `S.StateT Network.Gearman.Internal.GearmanClient IO a0' with actual type `IO GHC.Conc.Sync.ThreadId' In a stmt of a 'do' block: t <- W.runWorker gc (return ()) In the second argument of `($)', namely `do { g <- (W.registerWorker name func); t <- W.runWorker gc (return ()); return t >> return () } What do I wrong with W.runWorker gc (return ())? runWorker :: GearmanClient -> Gearman () -> IO ThreadId https://hackage.haskell.org/package/hgearman-0.1.0.2/docs/Network-Gearman-Wo... Best regards, Alexei