I have some exception types defined ...

data POSTOnlyException = POSTOnlyException

deriving ( Show, Typeable )

instance Exception POSTOnlyException

data BadPathException = BadPathException

deriving ( Show, Typeable )

instance Exception BadPathException

... and I want to use Data.Enumerator.catchError ...

catchError :: Monad m => Iteratee a m b -> (SomeException -> Iteratee a m b) -> Iteratee a m b

... so I define an error handler ...

handleErrors :: SomeException -> Iteratee a m String

handleErrors ex = case fromException ex of

Just POSTOnlyException -> return "POSTs only!"

Just BadPathException -> return "Bad path!"

_ -> return "Unknown exception!"

... but of course this doesn't compile, because the types of the LHSs in the case statement are different. I can get around it with some ugliness ...

handleErrors :: SomeException -> Iteratee a m String

handleErrors ex = case fromException ex of

Just POSTOnlyException -> return "POSTs only!"

_ -> case fromException ex of

Just BadPathException -> return "Bad path!"

_ -> return "Unknown exception!"

... but there must be a better way. Enlighten me?

Cheers,

Mike S Craig