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Within LTS Haskell 8.20 (ghc-8.0.2)

  1. waitUntilSTM :: TVar Bool -> STM ()

    Workflow Control.Workflow

    Wait until a certain clock time has passed by monitoring its flag, in the STM monad. This permits to compose timeouts with locks waiting for data using orElse

    • example: wait for any respoinse from a Queue if no response is given in 5 minutes, it is returned True.
    flag <- getTimeoutFlag $  5 * 60
    ap   <- step  .  atomically $  readSomewhere >>= return . Just  orElse  waitUntilSTM flag  >> return Nothing
    case ap of
    Nothing -> do logWF "timeout" ...
    Just x -> do logWF $ "received" ++ show x ...
    
    

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