Re: Changes to the type checker with respect to UndecidableInstances

2015-01-06 Thread 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 simo...@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-boun...@haskell.org] On Behalf Of Mitsutoshi
 Aoe
 Sent: 28 December 2014 10:47
 To: glasgow-haskell-users@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


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RE: Changes to the type checker with respect to UndecidableInstances

2014-12-30 Thread Simon Peyton Jones 
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-boun...@haskell.org] 
On Behalf Of Mitsutoshi Aoe
Sent: 28 December 2014 10:47
To: glasgow-haskell-users@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

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