GHC 7.10 regression when using foldr

Herbert Valerio Riedel hvr at
Tue Jan 20 23:02:48 UTC 2015

Hello Bryan,

On 2015-01-20 at 23:17:01 +0100, Bryan O'Sullivan wrote:


> For the record, it took me almost an hour to update attoparsec to fix all
> the various regressions, or to put it more charitably changes, introduced
> in GHC 7.10. I have twenty-something other packages to go through. I don't
> keep track of the time sunk from release to release, but this feels
> somewhat worse than average.

I'm a bit confused, several past attoparsec versions seem to build just
fine with GHC 7.10:

were there hidden breakages not resulting in compile errors?
Or are the fixes you mention about restoring -Wall hygiene?

> Basically, the more careful you are in writing a package, the more each
> update of GHC and base costs in nickel-and-dime tweaks to keep a build
> clean. It's not a very happy-making feedback loop. "Be a good citizen, and
> your reward is to spend *even more* time cleaning up!"


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