Data instances for MTL types

Ross Paterson ross at
Fri Jan 16 08:37:57 EST 2009

On Thu, Jan 15, 2009 at 10:46:46PM +0100, Henning Thielemann wrote:
> When trying to perform some tests with StrictCheck, I found that the  
> monads from the 'transformers' package don't have Data instances. Can 
> they be provided while keeping 'transformers' Haskell 98 and avoiding 
> orphan instances?

The Typeable and Data instances will be non-trivial, as they can't be
derived for higher-order type constructors.

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