Armin Groesslinger wrote:
> I think I have found an optimisation problem in GHC
> pre-4.07-20000613. [...]
Cool bug! :-) The example can be cut down further to:
----------------------------------------------------
main :: IO ()
main = print (length (filter (not . foo)
(filter (const False) [Nothing])))
where foo (Just x) = x
foo _ = error "foo"
----------------------------------------------------
After some experiments it seems that the RULE for filterFB is
the wrong:
"filterFB" forall c p q. filterFB (filterFB c p) q = filterFB c (\x -> p x && q x)
At least everything works when it is removed from the corresponding
interface file. Perhaps I'll have a closer look later.
Cheers,
Sven
