[Haskell-cafe] Safe Haskell and instance coherence

Mikhail Glushenkov the.dead.shall.rise at gmail.com
Thu Oct 11 16:42:40 CEST 2012


On Thu, Oct 11, 2012 at 4:33 PM, MigMit <miguelimo38 at yandex.ru> wrote:
> On Oct 11, 2012, at 6:23 PM, Mikhail Glushenkov <the.dead.shall.rise at gmail.com> wrote:
>> On Thu, Oct 11, 2012 at 3:54 PM, MigMit <miguelimo38 at yandex.ru> wrote:
>>> You have a bigger problem coming. Some extensions make multiple instances OK, even in Safe Haskell. For example:
>>> {-# LANGUAGE FlexibleInstances, IncoherentInstances, Safe #-}
>>> [...]
>> Safe Haskell already disallows OverlappingInstances.
> It doesn't. Overlapping instances are allowed in safe modules, provided that they won't be used in other modules.

I stand corrected. Still, I think that something will have to be done
about IncoherentInstances if the aforementioned restriction will be

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