Proposal: Extensible exceptions

Chris Kuklewicz haskell at
Fri Jul 4 10:52:32 EDT 2008

Ian Lynagh wrote:
> === Library function differences
> As far as the library functions are concerned, here are the main
> differences:
> The old and new types for catch are:
>     Old: catch ::                IO a -> (Exception -> IO a) -> IO a
>     New: catch :: Exception e => IO a -> (e         -> IO a) -> IO a
> i.e. catch can now catch any type of exception; we don't have to force
> all the different types of extension into one fixed datatype.

Is there any sane way to allow extending or building equivalents to these for 


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