Axel Simon wrote:
On 06.03.2010, at 18:19, Bertram Felgenhauer wrote:
ptrEqual' :: a -> a -> Bool ptrEqual' x y = case reallyUnsafePtrEquality# x y of 0# -> False 1# -> True
This is actually a pointer comparison. I believe it can produce false negatives though, because indirections are not followed. If that's correct, a false negative may be turned into a positive by garbage collection. So use with care.
Interesting. But if reallyUnsafePtrEquality# is a primitive, it is evaluated either before or after GC, so it can't compare a pointer from one generation with the next.
That is true. But besides GC, there is another source of indirections: updating a thunk with its final value if it's too large, or with a different thunk, which happens when an asynchronous exception is raised. regards, Bertram