[Haskell-cafe] Show instances for error messages (Was: Refactoring status)

[Lutz Donnerhacke]

* Henning Thielemann wrote:
> happen. Paradoxical. It would be interesting if it is possible to tunnel
> Show class dictionaries through to an 'error' like IO is tunneled to
> 'trace'.

unsafeShow :: (forall a . Show a => a) -> String