control-monad-exception

Explicitly typed, checked exceptions with stack traces

http://pepeiborra.github.com/control-monad-exception

Latest on Hackage:

0.11.4

This package is not currently in any snapshots. If you're interested in using it, we recommend adding it to Stackage Nightly. Doing so will make builds more reliable, and allow stackage.org to host generated Haddocks.

LicenseRef-PublicDomain licensed by Pepe Iborra

Maintained by [email protected]

This package provides explicitly typed, checked exceptions as a library.

Computations throwing different types of exception can be combined seamlessly.

Example

data Expr = Add Expr Expr | Div Expr Expr | Val Double
eval (Val x)     = return x
eval (Add a1 a2) = do
   v1 <- eval a1
   v2 <- eval a2
   let sum = v1 + v2
   if sum < v1 || sum < v2 then throw SumOverflow else return sum
eval (Div a1 a2) = do
   v1 <- eval a1
   v2 <- eval a2
   if v2 == 0 then throw DivideByZero else return (v1 / v2)

data DivideByZero = DivideByZero deriving (Show, Typeable)
data SumOverflow  = SumOverflow  deriving (Show, Typeable)

instance Exception DivideByZero
instance Exception SumOverflow

GHCi infers the following types

eval :: (Throws DivideByZero l, Throws SumOverflow l) => Expr -> EM l Double
eval `catch` \ (e::DivideByZero) -> return (-1)  :: Throws SumOverflow l => Expr -> EM l Double
runEM(eval `catch` \ (e::SomeException) -> return (-1))  :: Expr -> Double

In addition to explicitly typed exceptions this package provides:

Support for explicitly documented, unchecked exceptions (via Control.Monad.Exception.tryEMT).
Support for selective unchecked exceptions (via Control.Monad.Exception.UncaughtException).
Support for exception call traces via Control.Monad.Loc.MonadLoc. Example:


f () = do throw MyException
g a  = do f a

main = runEMT $ do g () `catchWithSrcLoc`
                       \loc (e::MyException) -> lift(putStrLn$ showExceptionWithTrace loc e)

-- Running main produces the output:

*Main> main
 MyException
   in f, Main(example.hs): (1,6)
      g, Main(example.hs): (2,6)
      main, Main(example.hs): (5,9)
      main, Main(example.hs): (4,16)