John, have you seen this?
http://haskell.galois.com/cgi-bin/haskell-prime/trac.cgi/wiki/Extensible
Exceptions
Cheers,
Simon
On 07 April 2006 15:34, John Goerzen wrote:
> Hello,
>
> One thing that bugs me about Haskell is that exceptions are not
> extensible.
>
> I don't know how to craft a good solution, but perhaps if I explain
> the problem well, someone would come up with one.
>
> In a language such as Python or Java, and exception is an object.
>
> Let's consider Python for a quick example. Python has an IOError
> exception. So if I want to write a handler that deals with IOErrors,
> that's easy enough.
>
> Now maybe I want to do something like report socket errors specially.
> I could define a SocketError class that subclasses IOError. I could
> take this further, and define a URLError that subclasses SocketError.
>
> Now the beauty of it is that I can:
>
> * Have a handler that catches URLErrors only and does nothing special
> with SocketErrors or IOErrors.
>
> * Have a handler -- perhaps not even mine -- that catches and works
> with IOErrors. Since SocketError and URLError are descendants of
> IOError, that handler will *automatically* work if I raise a
> SocketError or a URLError.
>
> I can see no such mechanism in Haskell. Haskell's I/O exceptions
> have a certain defined set of errors that they can report, and I
> can't subclass them and make them more specific for my purposes if I
> want. Ditto for all the others.
>
> The Dynamic exception support is necessary and good to have, but it
> also under-documented and can be complex. And of course, they still
> suffer from the same lack of extensibility
>
> Are there any suggestions on how we might improve this situation in
> Haskell?
>
> -- John
_______________________________________________
Haskell-prime mailing list
Haskell-prime@haskell.org
http://haskell.org/mailman/listinfo/haskell-prime
