[Haskell-cafe] Safe Haskell and instance coherence

[Mikhail Glushenkov]

Hello Simon,

On Thu, Oct 11, 2012 at 11:24 AM, Simon Marlow <marlowsd at gmail.com> wrote:
> On 08/10/2012 20:11, Mikhail Glushenkov wrote:
>> I couldn't find anything on the interplay between orphan instances and
>> Safe Haskell both in the Haskell'12 paper and online. Is this
>> something that the authors of Safe Haskell are aware of/are intending
>> to fix?
>
> [...]
> I don't know what we should do about this.  Disallowing orphan instances
> seems a bit heavy-handed. David, Simon, any thoughts?

What about detecting duplicate instances at link time? We could put
information about all instances defined in a given module into the
.comment section of the corresponding .o file and then have a pre-link
step script extract this information from all .o files in the program
and check that there are no duplicate or conflicting instances.


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