#2467: orphan instance warnings are badly behaved
---------------------------------+------------------------------------------
Reporter: duncan | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 6.12 branch
Component: Compiler | Version: 6.8.2
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Os: Unknown/Multiple
Architecture: Unknown/Multiple |
---------------------------------+------------------------------------------
Comment (by Syzygies):
It came up in my code that I needed
> instance Foldable ((,) a) where foldr f z (_,y) = f y z
which is completely parallel to the Functor instance, but unlike the
Functor instance is not provided by the standard libraries.
There is no way that this instance can be anything but an orphan in my
code (I shouldn't change Data.Foldable on a whim, it would make my code
non-portable), so in this case I would argue that it is wrong for -Wall
-Werror to abort compilation over this. I added -fno-warn-orphans, but
that is a clunky fix which now deprives me of that warning when it might
be relevant.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2467#comment:7>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
_______________________________________________
Glasgow-haskell-bugs mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
