Overlapping and incoherent instances

[Herbert Valerio Riedel]

On 2014-07-29 at 14:13:22 +0200, Richard Eisenberg wrote:
> Are folks very keen to have *warning-free* compilation on several GHC
> versions? Personally, I would aim for warning-free compilation on a
> most recent version, and otherwise successful compilation on older
> versions.

IMO: In typical build-bot configurations where you test against multiple
GHC versions you often the warnings to be turned into errors via
-Werror, as otherwise you wouldn't notice them. After all, warnings are
hints about something that may need to be looked at, and if they turn
out to be harmless, the specific warning can be turned off on a
case-by-case basis (which alas, in GHC's case is a bit difficult, as for
instance, you can't turn off a specific warning for a single declaration
only, but only for a whole module)

Cheers,
  hvr