Re: [Haskell-cafe] GHC API: type class instance check

Yes, that's true, but suppose we have module M where import OtherModPossiblyWithInstance Then as far as I understand, the compiler will have processed OtherModPossiblyWithInstance already and the existence of class instances in OtherModPossiblyWithInstance should be know.

On 11 Nov 2016, at 10:07, MigMit wrote:

I'm no expert in GHC plugins, but isn't it true that class instances can be added in other modules? So that this information is simply not available when compiling one?

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On 11 Nov 2016, at 08:57, J. Stutterheim wrote:

Hi all,

I'm writing a core-to-core GHC plugin and have two questions:

- Given some t :: Type, how can I check whether there exists an instance of some type class C for t? - How can I check whether some type class C exists, and if so, how can I get a value c (presumably :: Class) of this class?

Thanks!

- Jurriën_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.