http://hackage.haskell.org/trac/ghc/ticket/7913

nubBy.hs

Replying to [comment:3 simonpj]:  -- http://hackage.haskell.org/trac/ghc/ticket/7913

`nubBy` and `nub` are both intuitively ''left'' scans. `nub` should behave like 
`concatMap fst . scanl (\(_,prevs) new-> if not (((elem new prevs))) then 
([new],new:prevs) else ([],prevs)) ([],[])`. 

`nub` should be the same as `nubBy (==)`.

Report is consistent in this regard, as it also defines `elem x = any (== x)`, 
as well as
{{{
  nubBy eq (x:xs) = x : nubBy eq (filter (\ y -> not (eq x y)) xs)
                                                     --  ^^^ older newer 
}}}

Looks like it must be changed, although this will break existing code 
(e.g. {{{nubBy (((==0).).rem) [2..]}}} ).