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AsyncGotchas.hs
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/
AsyncGotchas.hs
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module AsyncGotchas where
import Control.Concurrent (threadDelay)
import Polysemy
import Polysemy.Async
import Polysemy.Error
failing :: Members '[Error (), Embed IO] r => Sem r Int
failing = do
embed $ putStrLn "Failing"
throw ()
actFailing :: Members '[Error (), Embed IO, Async] r => Sem r ()
actFailing = do
a <- async failing
embed $ threadDelay 250
embed $ putStrLn "Do stuff"
r <- await a
embed $ putStrLn "Do even more stuff"
embed $ print r
working :: Members '[Error (), Embed IO] r => Sem r Int
working = do
embed $ putStrLn "Working"
return 42
actWorking :: Members '[Error (), Embed IO, Async] r => Sem r ()
actWorking = do
a <- async working
embed $ threadDelay 250
embed $ putStrLn "Do stuff"
r <- await a
embed $ putStrLn "Do even more stuff"
embed $ print r
main :: IO ()
main = do
runM (runError @() $ asyncToIO actFailing) >>= print
threadDelay 250
runM (runError @() $ asyncToIO actWorking) >>= print