Hi Simon,

On Sat, Feb 9, 2013 at 12:18 AM, Simon Peyton-Jones <simonpj@microsoft.com> wrote:

Yes do point me to where the check for deriving(Typeable) is awkard to test against AutoDeriveTypeable.

I add the instances in line 319 of TcDeriv. It's easy to add them here, because I just need to
produce a simple DerivDecl. However, checking if there are instances defined already is
cumbersome, because I'd have to look at both the inst_decls and the deriv_decls, while
being careful to keep duplicates, because those are "real" errors.

In general, I find it hard to extract the class and type from an InstDecl or a DerivDecl, because
these are just HsTypes in the end, so I'd have to go deconstruct the HsType and hope it would
have the right shape. But maybe there are some auxiliary functions that I missed?

Thanks,
Pedro