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module Main where
import Control.Exception
import System.IO.Error
main = do
ioTest
errorTest
noMethodTest
patMatchTest
guardTest
ioTest :: IO ()
ioTest = catchJust (\e -> if isUserError e then Just () else Nothing)
(ioError (userError "wibble"))
(\() -> putStrLn "user exception caught")
errorTest :: IO ()
errorTest = do r <- try (evaluate (1 + error "call to 'error'"))
case r of
Left (ErrorCall _) -> putStrLn "error call caught"
Right _ -> error "help!"
instance (Show a, Eq a) => Num (Maybe a) where {}
noMethodTest :: IO ()
noMethodTest = do r <- try (evaluate (Just () + Just ()))
case r of
Left (NoMethodError err) -> putStrLn "no method error"
Right _ -> error "help!"
patMatchTest :: IO ()
patMatchTest = catch (case test1 [1..10] of () -> return ())
(\ex -> case ex of
PatternMatchFail err -> putStr err
_ -> error "help!")
test1 [] = ()
guardTest = catch (case test2 of () -> return ())
(\ex -> case ex of
PatternMatchFail err -> putStr err
_ -> error "help!")
test2 | all (==0) [1] = ()
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