Complete chapter 30

30-when-things-go-wrong/30-when-things-go-wrong.md

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+# 30 When things go wrong
+
+## 30.5 The unbearable imprecision of trying
+
+see [src/StoppingTheParty.hs](./src/StoppingTheParty.hs)

30-when-things-go-wrong/src/StoppingTheParty.hs

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+module StoppingTheParty where
+
+import Control.Concurrent(threadDelay)
+import Control.Exception
+import Control.Monad (forever)
+import System.Random (randomRIO)
+
+randomException :: IO ()
+randomException = do
+    i <- randomRIO (1, 10 :: Int)
+    if i `elem` [1..9]
+        then throwIO DivideByZero
+        else throwIO StackOverflow
+
+main :: IO ()
+main = forever $ do
+    let tryS :: IO () -> IO (Either SomeException ())
+        tryS = try
+    _ <- tryS randomException
+    putStrLn "Live to loop another day!"
+    threadDelay (1 * 1000000)