[Haskell-cafe] Obscure instances for Obscure types

Nicolas Frisby nicolas.frisby at gmail.com
Thu Apr 26 18:28:36 EDT 2007

I've had a similar question, which I think boiled down to a
compilation issue. Consider packages A and B that can be defined
independently. But, just as Neil pointed out, perhaps A and B could
also interact beyond their basic definition.

My naive idea is that A would compile the simple independent way if B
wasn't around and vice versa. But if A and B were both present at
compile time, then their interaction would also be compiled. The open
question is then where does that interaction live?

I would guess this problem has been solved in other systems. Anything
come to mind?

On 4/26/07, Neil Mitchell <ndmitchell at gmail.com> wrote:
> Hi
> I currently maintain two libraries, TagSoup which defines the Tag data
> type, and BinaryDefer, which defines the BinaryDefer class. If I
> wanted to include an instance for BinaryDefer Tag, where would I put
> it?
> Putting it in either library introduces an artificial dependency on
> the other. Putting it in a separate libary makes the library about 4
> lines long and is just annoying. Putting it in the individual
> application(s) is exactly what libraries were designed to avoid.
> Is there a solution?
> Thanks
> Neil
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