Would you say this the same as the one described in the user guide? http://www.haskell.org/ghc/docs/latest/html/users_guide/bugs.html#bugs-ghc GHC's inliner can be persuaded into non-termination using the standard way to encode recursion via a data type: data U = MkU (U -> Bool) russel :: U -> Bool russel u@(MkU p) = not $ p u x :: Bool x = russel (MkU russel) We have never found another class of programs, other than this contrived one, that makes GHC diverge, and fixing the problem would impose an extra overhead on every compilation. So the bug remains un-fixed. There is more background in Secrets of the GHC inliner. Duncan On Sun, 2007-02-04 at 13:49 +0000, Wouter Swierstra wrote:
When I try to compile to the following program, GHC seems to loop:
data Evil = Evil (Evil -> Evil)
instance Show Evil where show _ = "t"
apply :: Evil -> Evil -> Evil apply (Evil f) x = f x
delta :: Evil delta = Evil (\x -> x `apply` x)
omega :: Evil omega = delta `apply` delta
main = print omega
The program codes up a non-terminating term omega - very similar to (\x -> x x) (\x -> x x) - without using recursion. The trick is to define an Evil data type which has a negative occurrence of Evil.
I realize it's a contrived example, but I wasn't sure if it's a known issue. In case it matters, I'm using GHC 6.6 on a PowerPC Mac.
All the best,
Wouter