GHC 7.0.1 rc1: Could not deduce (Typeable a) from the context (Typeable a, …)

Malte Sommerkorn malte.sommerkorn at
Thu Sep 30 10:55:09 EDT 2010

Simon Peyton-Jones wrote:
> Oh dear, that really is quite a strange error message. Something is
> definitely wrong. Can you please make a ticket for it, and include
> instructions on how to reproduce it? 


> I gather that it depends on other packages that themselves needed changes,
> so reproduction might not be entirely easy?

I've attached a module to the bug report that triggers the problem and only
depends on base and mtl, so that should be fairly easy to reproduce.


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