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control-monad-exception-0.4.2: Explicitly typed, checked exceptions with stack traces

The control-monad-exception package

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

New in version 0.4: * (optionally) Unchecked exceptions (with UncaughtException) * Exception stack traces (with WithSrcLoc). Example

 f () = $withLocTH $ throw MyException
 g a  = $withLocTH $ f a

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

Running main produces the output:

 *Main> main
 MyException
  in Main.docatch.hs: (12,6)
     Main.docatch.hs: (11,7)

Properties

Modules

Downloads

• control-monad-exception-0.4.2.tar.gz (Cabal source package)
• package description (included in the package)

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