On Sun, Mar 01, 2009 at 02:30:34PM -1000, Tim Newsham wrote:

Did nubBy change recently? In 6.8.2 I could generate primes as:

nubBy (\a b -> b `mod` a == 0) [2..]

but in 6.10.1 I have to use

nubBy (\a b -> a `mod` b == 0) [2..]

Is this change intentional? If so, what is the reason?

Tue Sep 2 10:29:50 BST 2008 Simon Marlow * #2528: reverse the order of args to (==) in nubBy to match nub This only makes a difference when the (==) definition is not reflexive, but strictly speaking it does violate the report definition of nubBy, so we should fix it. See also: http://hackage.haskell.org/trac/ghc/ticket/2528 http://www.haskell.org/onlinereport/list.html#sect17.6 The Report imposes the precondition that the relation be an equivalence, so your use was out of spec. Still, perhaps it would have been better to fix #2528 by changing nub instead of nubBy. As it is the USE_REPORT_PRELUDE versions of nub and nubBy differ from the faster versions. (And the comment on elem_by is untrue.)