Initial data commit

Task/Metronome/Haskell/metronome.hs

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+import Control.Concurrent
+import Control.Concurrent.MVar
+import System.Process (runCommand)
+
+-- This program works only on the GHC compiler because of the use of
+-- threadDelay
+
+data Beep = Stop | Hi | Low
+
+type Pattern = [Beep]
+
+type BeatsPerMinute = Int
+
+minute = 60000000 -- 1 minute = 60,000,000 microseconds
+
+-- give one of the following example patterns to the metronome function
+
+pattern4_4 = [Hi, Low, Low, Low]
+pattern2_4 = [Hi, Low]
+pattern3_4 = [Hi, Low, Low]
+pattern6_8 = [Hi, Low, Low, Low, Low, Low]
+
+-- use this version if you can't play audio, use Windows or don't
+-- have audio files to play
+-- beep :: Beep -> IO ()
+-- beep Stop = return ()
+-- beep Hi = putChar 'H'
+-- beep Low = putChar 'L'
+
+-- use this version if you can and want to play audio on Linux using
+-- Alsa. Change the name of the files to those of your choice
+
+beep Stop = return ()
+beep Hi = putChar 'H' >> runCommand "aplay hi.wav &> /dev/null" >> return ()
+beep Low = putChar 'L' >> runCommand "aplay low.wav &> /dev/null" >> return ()
+
+tick :: MVar Pattern -> BeatsPerMinute -> IO ()
+tick b i = do
+    t <- readMVar b
+    case t of
+        [Stop] -> return ()
+        x -> do
+            mapM_ (\v -> forkIO (beep v) >> threadDelay (minute `div` i)) t
+            tick b i
+
+metronome :: Pattern -> BeatsPerMinute -> IO ()
+metronome p i = do
+    putStrLn "Press any key to stop the metronome."
+    b <- newMVar p
+    _ <- forkIO $ tick b i
+    _ <- getChar
+    putMVar b [Stop]