Using GADT in exception handling

Question

Here's my problem

I'm using Control.Exception.catch for my exception handling, which has the following type: (culled from Hoogle)

catchSource
:: Exception e   
=> IO a 
The computation to run
-> (e -> IO a)  
Handler to invoke if an exception is raised
-> IO a  

Here is the constructor I will be passing to my handler function

> data JobException = PreProcessFail
>                   | JobFail
>                   | ChartFail
>                       deriving (Show, Typeable)

> instance Control.Exception JobException

Here is the Handler function as it is right now :

> exceptionHandler :: JobException -> IO ()
> exceptionHandler exception = do
>    writeFile "testException.txt" ("caught exception " ++ show exception )

I'm going to use this to do some logging. The information I need to log will be in a record of type JobState

> type JobState = MVar ProcessConfig

> data ProcessConfig = PConfig { model :: ServerModel
>                              , ipAddress :: String
>                              , cookie :: Cookie
>                              } deriving Show

So since I need a handler that is forced to have the type I mentioned above, and I need a JobState, I thought the answer would be to rewrite JobException to hide a JobState inside it. That seems to be a job for GADT! I'm not sure, this is new territory.

Am I right? Can I solve this with a GADT? Could someone provide a clue in how to begin to construct one? The tutorials I have been reading assume you're trying to solve a more complicated problem than what I have got.

If I am wrong, could someone point me in the right direction?

update: I learned about dynamic types from 1 and found shortly thereafter Data.Dynamic. Getting warmer?

Fun With Phantom Types