[darcs-users] darcs patch: Remove unused import. (and 7 more)

Trent W. Buck trentbuck at gmail.com
Wed Jul 1 00:26:12 UTC 2009

Jason Dagit <dagit at codersbase.com> writes:

> On Fri, Jun 26, 2009 at 12:36 AM, Trent W.Buck <trentbuck at gmail.com> wrote:
>> Hopefully these remove the GHC warnings without breaking anything.
>> [...]
>> Fri Jun 26 16:03:07 EST 2009  Trent W. Buck <trentbuck at gmail.com>
>>  * Keep GHC quiet about orphaned typeclass instances in Darcs.Gorsvet.
>>  This should actually be fixed by moving these instances to another
>>  module, because as GHC's user manual says:
>>    The trouble with orphans is that GHC must pro-actively read the
>>    interface files for all orphan modules, just in case their instances
>>    or rules play a role, whether or not the module's interface would
>>    otherwise be of any use. See Section 4.6.12, “Orphan modules and
>>    instance declarations” for details.
> There was a thread in the last 3 months or so on Haskell-Cafe about
> orphan instances and, in particular, if they cause any problems in
> practice.  I admit I didn't read the thread.  We have them in lots of
> places through out the darcs code.  Personally, I've never really
> understand what it's all about or why I would want to remove them.  As
> far as I know, we've never had problems (read: bugs) because of them.

My reading of the GHC documentation was that it doesn't cause "bugs",
but rather it forces GHC to do more work, or be less parallelized.  My
goal with these patches was to remove (spurious) warnings from the 2.3b2
build.  Since I'm hiding (instead of fixing) what appears to be a
legitimate (if minor) complaint, I wanted to make sure that people
reviewing change history could find the associated compiler docs.

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