Merging polykinded typeable

José Pedro Magalhães jpm at
Wed Feb 13 11:56:11 CET 2013

Hi Simon,

On Sat, Feb 9, 2013 at 12:18 AM, Simon Peyton-Jones
<simonpj at>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

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