[Haskell-cafe] Introducing Instances in GHC point releases

John Goerzen jgoerzen at complete.org
Fri May 22 09:26:21 EDT 2009

Henning Thielemann wrote:
> John Goerzen schrieb:
>> So this is annoying (CCing -cafe)
>> I need NominalDiffTime and UTCTime to have Typeable instances.  In
>> 6.10.1, they didn't ship with them out of the box, so I added them.
>> Apparently, in 6.10.3, they DO ship with those instances out of the box.
>> Annoyingly, that means that my code breaks on 6.10.3.
> After having conflicting instances several times with some types in the
> past, I came to the conclusion that I should never define orphan
> instances. Can you restrict your package to 6.10.3 where an "official"
> instance is available?
> http://www.haskell.org/haskellwiki/Orphan_instance

I didn't care about presenting the instance to people using my library,
but the instance was necessary within the library itself, and led to the
compilation error.

-- John

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