On Wed, Aug 13, 2014 at 7:33 AM, Duncan Coutts wrote: So it's true that using flags here is the standard solution (e.g. as
was used with the base split for a few years), so many (but not all)
users know this already. I should also note (Andres: please correct me if I'm wrong) that as of
cabal-install 1.20, the cost in terms of backtracking for flags like
these is now quite small because choosing them is deferred as late as
possible. Edward: this should solve your problem with flags with
transformers, at least once 1.20 is widely used. It'd be great if you
could check that this is the case. Right now I'm stuck supporting people who use some very old cabal installs,
so it'll be a long long time in my case. :)
I find myself a bit gunshy here as every time I use a flag I get a
complaint from somewhere.
The experience trying and failing to fix the use of flags in
transformers-compat has left me personally somewhat sworn off non manual
flags for now. AFAIK, we didn't actually fix the bug there with the first
try or two, but Andres may have managed to fix it after I gave up. There is
was admittedly a different issue with the backtracker missing a case.
I'm happy to go along with the plan, but I confess I suspect it'll lead to
at least one bug report somewhere, and if it doesn't I'll just enjoy the
pleasant surprise. =)
-Edward