Changes to the type checker with respect to UndecidableInstances

[Mitsutoshi Aoe]

Hi Simon,

Thanks. So there was a bug in the type checker. Do you have a link to
the ticket or commits which fixed the issue?

Mitsutoshi

2014-12-30 19:56 GMT+09:00 Simon Peyton Jones <simonpj at microsoft.com>:
> UndecidableInstances is supposed to be needed if GHC can’t prove that the
> instance declarations terminate.  But here it can be sure they terminate.
> GHC 7.6.3 didn’t realise this.
>
>
>
> I’ll modify the user manual to be clearer on this point.
>
>
>
> Simon
>
>
>
> From: Glasgow-haskell-users
> [mailto:glasgow-haskell-users-bounces at haskell.org] On Behalf Of Mitsutoshi
> Aoe
> Sent: 28 December 2014 10:47
> To: glasgow-haskell-users at haskell.org
> Subject: Changes to the type checker with respect to UndecidableInstances
>
>
>
> Hi,
>
>
>
> I found a difference between GHC 7.6.3 and 7.8.3 with respect to
> UndecidableInstances.
>
>
>
> https://gist.github.com/maoe/57a4346eb36aee159916
>
>
>
> 7.6.3 requires UndecidableInstances to compile this snippet whereas 7.8.3
> doesn't. What has changed in the type checker?
>
>
>
> Mitsutoshi
>
>