throwable-exceptions gives the easy way to throw exceptions.

:diamonds: throwable-exceptions :diamonds:

throwable-exceptions gives an easy way to create the data types of Exception instance with TemplateHaskell, and gives simple data types of Exception instance with its value constructor, for your haskell project :dog:

• throwable-exceptions is available in
  • Hackage
  • stackage (nightly build)

:books: Document is available in here :books:

• throwable-exceptions - Hackage

:muscle: Why should we use this ? :muscle:

We want to throw some exception frequently, but the mostly throwable exceptions are not given by base.
throwable-exceptions complements it :+1:

Examples

• vvv The summary of the exact examples is available here vvv
  • test/MainTest.hs

You can create a data type of Exception instance by a line :exclamation:

{-# LANGUAGE TemplateHaskell #-}
module Main where

-- This is same as
--
-- data MyException a = MyException
--  { myExceptionCause :: String
--  , myExceptionClue  :: a
--  } deriving (Show, Typeable)
-- instance (Typeable a, Show a) => Exception (MyException a)
--
declareException "MyException" ["MyException"]

-- This is same as
--
-- data TwoException a =
--  FirstException
--    { firstExceptionCause :: String
--    , firstExceptionClue  :: a
--    } |
--  SecondException
--    { secondExceptionCause :: String
--    , secondExceptionClue  :: a
--    } deriving (Typeable)
--
-- instance Show a => (TwoException a) where
--  ...
-- instance (Typeable a, Show a) => Exception (TwoException a)
--
declareException "TwoException" ["FirstException", "SecondException"]

main :: IO ()
main = do
  print $ ([1..4] `at` 5 :: Either SomeException Int)
  print $ MyException "hi" 10
  print $ myException "poi"
  print $ firstException "chino"
  print $ secondException "cocoa"

• the completely example
  • in example/Main.hs

Several exceptions are defined by default :smile:

For example, IOException's value constructor is not given :cry:
But you can use Control.Exception.Throwable.IOException' instead :dog:

module Main where

main :: IO ()
main = do
  throwM $ IOException' "oops!" "in main"
  throwM $ ioException' "oops!"

:+1:

PR is welcome !