Re: PROPOSAL: re-export 'Typeable' type-class from Prelude

On Thu, Sep 11, 2014 at 4:25 PM, Brandon Allbery wrote:

On Thu, Sep 11, 2014 at 10:17 AM, Henning Thielemann wrote:

...

Am 11.09.2014 um 16:11 schrieb Felipe Lessa:

...

On 11-09-2014 11:05, Michael Snoyman wrote:

...

The one case I think Typeable should *always* be around for is creating new instances of Exception. The fact that AutoDeriveTypeable doesn't require Typeable in Prelude lessens my +1 a bit down to a +0.5, but I really want it to be easier for people to define their own exception types.

That's an argument for exporting Typeable from Control.Exception, since Prelude does not export Exception and friends.

For me the Typeable constraint of the Exception class is just an argument to not use implicit exceptions of IO, but instead use one of the various Exception monads with explicit exception types.

Not to mention that "...want it to be easier for people to define their own exception types" really makes me think something's gone wrong with the design somewhere. Exceptions ought to be ... exceptional, not common enough that people regularly need to define their own.

I thought the whole point of extensible exceptions was to define your own? That way you can catch them, instead of just piling them all together. I get that there are people who think you shouldn't use exceptions at all, but for the people who *do* use them, I think they should almost always define a new type for each one. Erik