throwable-exceptions: throwable-exceptions gives the exception's value constructors

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throwable-exceptions gives the exception's value constructors

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Dependencies base (>=4.7 && <5), safe-exceptions [details]
License MIT
Copyright aiya000
Author aiya000
Category Simple
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Uploaded by aiya000 at Mon Jun 12 02:22:11 UTC 2017
Distributions LTSHaskell:, NixOS:, Stackage:
Downloads 2911 total (100 in the last 30 days)
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Status Hackage Matrix CI
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Last success reported on 2017-06-12 [all 1 reports]




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: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's value constructor is not given.

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: