39 lines
908 B
Haskell
39 lines
908 B
Haskell
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module Debouncer (debounced) where
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import Control.Monad.Catch
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import Control.Monad
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import Control.Concurrent
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-- | Ensure the function is run in single thread, w/o overlapping.
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--
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-- If called concurently, everyone will get results of the winner.
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--
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-- If called, waits for next result to arrive.
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--
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-- If function throws an error, will rethrow it in caller thread.
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--
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debounced :: forall s r. (s -> IO r) -> IO (s -> IO r)
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debounced act = do
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i <- newEmptyMVar
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o <- newEmptyMVar
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mask_ do
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forkIO do
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forever do
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_ <- tryTakeMVar o
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i' <- takeMVar i
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o' <- try $ act i'
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putMVar o (o' :: Either SomeException r)
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return $ \i' -> do
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_ <- tryTakeMVar i
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putMVar i i'
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readMVar o >>= either throwM return
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test :: IO ([Int] -> IO Int)
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test = debounced \s -> do
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threadDelay 2000000
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unless (odd (length s)) do
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error "even"
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return (length s)
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