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

Brandon Allbery allbery.b at
Thu Sep 11 14:25:33 UTC 2014

On Thu, Sep 11, 2014 at 10:17 AM, Henning Thielemann <
schlepptop at> 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.

brandon s allbery kf8nh                               sine nomine associates
allbery.b at                                  ballbery at
unix, openafs, kerberos, infrastructure, xmonad
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