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 at me.com
Tue Sep 20 13:32:26 CEST 2011
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
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.
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