[Haskell-cafe] Exportable and importable instances

Gábor Lehel illissius at gmail.com
Fri Jan 7 14:21:58 CET 2011

The objection to this I recall hearing is that it would make it
possible for different parts of the program to see different instances
for a given type (local instances, effectively), which would have
"interesting" results. I don't know if there's a way to implement the
feature which avoids this, or whether also adding support for local
instances is actually part of the plan. (If I'm thinking this through
correctly, this is currently avoided because instances are always
exported, and Main imports all modules transitively, so any
conflicting instances will be visible in Main at the latest.)

On Fri, Jan 7, 2011 at 2:07 PM, Marco Túlio Gontijo e Silva
<marcot at marcot.eti.br> wrote:
> Hi.
> I'm planning to propose a language extension for Haskell to make it possible to
> control the visibility of type class instances in module export and import
> lists as a research project.  I'm planning to implement this in GHC.  I've
> already mentioned it in #ghc at irc.freenode.net and got interesting comments from
> tibbe and quicksilver.
> I'd be glad to receive more feedback on the idea.  If you have any
> comments, please reply to this thread or mail me individually, at your will.
> Greetings.
> --
> marcot
> http://marcot.eti.br/
> [Flattr=54498]
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