Proposal: Extensible exceptions

John Meacham john at
Tue Jul 15 18:40:23 EDT 2008

On Fri, Jul 04, 2008 at 02:29:24PM +0100, Ian Lynagh wrote:
> Also, currently it derives Data.Typeable, which is unportable, but we
> can easily work around that. The only extensions that I don't think that
> we can do without are ExistentialQuantification and Rank2Types.
> DeriveDataTypeable makes the implementation easier, and
> DeriveDataTypeable and PatternSignatures make using it easier.

If Typeable is going to be in the language, then I think 'deriving
Typeable' should not only be included, but be the _only_ way to get
Typeable instances. There is a lot of room for compiler specific
representations of TypeRep's and a lot of codes invarients can be broken
by nasty Typeable instances. Though, this is more a haskell' issue. But
I have no qualms about using DeriveDataTypeable in code if I am going to
be using Typeable at all.


John Meacham - ⑆⑆john⑈

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