Please apply the comparison function given to nubBy to elements of the list in the order in which they occur in the list.

[Christian Maeder]

Am 20.09.2011 20:21, schrieb Edward Kmett:
[...]
> I would suggest you rephrase this as a formal proposal, then I can
> happily vote +1.

Seeing the "wonderful" interrelation between elem, nub, nubBy and i.e.

   unionBy eq xs ys =  xs ++ foldl (flip (deleteBy eq)) (nubBy eq ys) xs

   intersectBy eq xs ys =  [x | x <- xs, any (eq x) ys]

(note that "any (eq x)" could be "elemBy eq")

I see hardly a chance to make a sensible proposal.

I think, it is wrong to change the implementation of "elem" and 
"notElem" since I expect the "key" to be the first argument of the 
eq-comparison (in contrast to the REPORT_PRELUDE!).

But this all would not matter if the eq-function are always symmetric, 
which may be not the case in practise. So a change could break existing 
code.

> I'd also suggest rephrasing rhe mapAccumR as a formal proposal. I'm not
> sure yet of whether or not I'd be behind that one, but make both
> proposals separately, so they can pass individually.

I also don't see a relation to mapAccumR, so why don't you make such a 
separate proposal?

C.