# :diamonds: throwable-exceptions :diamonds:
throwable-exceptions gives the exception's value constructors for your haskell project :dog:


# :muscle: Why we should use this ? :muscle:
The situation that we want to throw the specific exception is happened frequently,
but many general exceptions are not given by base.

For example, [IOException](https://hackage.haskell.org/package/base-4.9.1.0/docs/Control-Exception.html#t:IOException)'s value constructor is not given.

```haskell
import Control.Exception.Safe (MonadThrow, throwM, IOException(..), try, Exception, SomeException)
import Control.Monad.IO.Class (MonadIO, liftIO)
import Control.Monad.Trans.Either (runEitherT)

readFileOrError :: (MonadThrow m, MonadIO m) => FilePath -> m String
readFileOrError path = do
  xOrErr <- liftIO . try $ readFile path
  case xOrErr of
    Left e -> throwM . IOException $ show (e :: SomeException)
    Right a -> return a

main :: IO ()
main = do
  xOrErr <- runEitherT $ readFileOrError "Main.hs"
  case xOrErr of
    Left e -> putStrLn $ "oops: " ++ show (e :: SomeException)
    Right a -> putStrLn a

-- Result output vv
-- Data constructor not in scope: IOException :: [Char] -> e1
```

But you have not to define a specific exception yourself
if you use this :muscle: