Preventing manual instances

Joachim Breitner mail at
Mon Sep 9 07:25:01 UTC 2013

Dear Predro,

Am Sonntag, den 08.09.2013, 18:27 -0500 schrieb Austin Seipp:
> I know Pedro committed the work to make manual
> Typeable instances an error, which is great.

the Coercible class has a similar property, and I added the check to
prevent manual instances to checkValidInstance in TcValidity:
while you did it in tcInstDecls1 in TcInstDecls:;a=commitdiff;h=5335e56953c4bbe18166039c06256e725f074b64

I’m happy to follow suite if you tell me that TcInstDecls is indeed the
better spot for such a check.


Joachim “nomeata” Breitner
  mail at joachim-breitner.de
  Jabber: nomeata at  • GPG-Key: 0x4743206C
  Debian Developer: nomeata at
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