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

[Malcolm Wallace]

If this is a _proposal_ to change ghc's non-Report-compatible Data.List implementation to match the behaviour of the Report implementation, then count me as a +1.

> I think an important convention when it comes to higher order
> functions on lists is that to the extent which is possible, the
> function parameters take elements from the list (or things computed
> from those) in the order in which they occur in the original list.

This seems like an entirely reasonable principle.

> I'm aware that the Report (strangely!) explicitly leaves the behaviour
> of nubBy unspecified for functions which are not equivalence
> relations, but the behaviour given by the Report implementation (the
> opposite of the current behaviour in GHC) is useful and desirable
> nonetheless.

I notice that the Haskell'98 Report gives a sample implementation, but the Haskell'2010 Report does not.  I wonder if this is a regression, since in days of yore, the Report implementation was treated as a gold standard reference for questions about function semantics, strictness and so forth.


Regards,
    Malcolm