Hi,
I have tested it in GHC 6.10.4 (Win XP) and GHC 6.8.3 (Linux), both give the wrong result (categaried):
7 <= 3 ?: False 3 <= 5 ?: True 3 <= 9 ?: True 3 <= 6 ?: True 3 <= 8 ?: True 3 <= 3 ?: True 3 <= 5 ?: True 3 <= 4 ?: True [[7],[3,5,9,6,8,3,5,4]] What exactly is wrong with this result? All of the above comparisons seem to get the right result, and they say 7 is not in the same categorie as 3, but all other numbers are in the same category as 3. So the returned list looks ok too.
Perhaps you had expected another output list (please tell us what you think you've found a bug!)? In fact, it seems that any output list would have been correct, since you're using a comparison function that is not symmetrical. In other words, you're say 7 should be in the same category as 3, but 3 should not be in the same category as 7. Since nothing is guaranteed about the order in which groupBy compares elements, any grouping could be achieved by letting groupBy choose the "right" ordering. So, it seems your comparison function is wrong since it does not satisfy the (unwritten) requirement of symmetry? Gr. Matthijs