Yes, I did too :-) But there is a key difference in this case, all these definitions are mathematically equivalent with identical semantics instead of being some fuzzy subjective standards.
-harendra On 5 February 2018 at 23:46, Brandon Allbery <allber...@gmail.com> wrote: > Why do I suddenly catch a whiff of https://xkcd.com/927/ ? > > On Mon, Feb 5, 2018 at 1:13 PM, Harendra Kumar <harendra.ku...@gmail.com> > wrote: > >> According to hayoo there seem to be 7 different implementations of this >> same function. Yours is 8th and mine is 9th and other people may have more >> not uploaded or maybe the ones that hayoo is not able to find. Does that >> make a case for including this in some standard place? >> >> -harendra >> >> On 5 February 2018 at 12:22, Evan Laforge <qdun...@gmail.com> wrote: >> >>> I have my own list library with a bunch of things like this. I think >>> it's what most people do, and some upload them to hackage, e.g. >>> utility-ht or the split package, or data-ordlist. >>> >>> Specifically, I think rollingGroupBy is what I call splitWith: >>> >>> -- | Split @xs@ before places where @f@ matches. >>> -- >>> -- > split_with (==1) [1,2,1] >>> -- > --> [[], [1, 2], [1]] >>> split_with :: (a -> Bool) -> [a] -> NonNull [a] >>> -- ^ output is non-null, and the contents are also, except the first >>> one >>> >>> You can probably find something like this in 'split', or if not, that >>> might be a good place to contribute it. >>> >>> I have a bunch of grouping functions too, which I use all the time, so >>> if there's some kind of general list grouping package then maybe I >>> could put them there. >>> >>> On the other hand, this sort of thing is pretty individual, so it >>> doesn't seem so bad for each person to have their own local library. >>> That way you know it fits your style. Ultimately I think that's why >>> none of the split functions made it into Data.List, every person has a >>> slightly different idea of what it should be. >>> >>> On Sun, Feb 4, 2018 at 7:50 PM, Harendra Kumar <harendra.ku...@gmail.com> >>> wrote: >>> > Hi, >>> > >>> > For a small problem, I was looking for a groupBy like function that >>> groups >>> > based on a predicate on successive elements but I could not find one. I >>> > wrote these little functions for that purpose: >>> > >>> > -- | Like span, but with a predicate that compares two successive >>> elements. >>> > The >>> > -- span ends when the two successive elements do not satisfy the >>> predicate. >>> > rollingSpan :: (a -> a -> Bool) -> [a] -> ([a], [a]) >>> > rollingSpan _ xs@[] = (xs, xs) >>> > rollingSpan _ xs@[_] = (xs, []) >>> > rollingSpan p (x1:xs@(x2:_)) >>> > | p x1 x2 = >>> > let (ys, zs) = rollingSpan p xs >>> > in (x1 : ys, zs) >>> > | otherwise = ([x1], xs) >>> > >>> > -- | Like 'groupBy' but with a predicate that compares two successive >>> > elements. >>> > -- A group ends when two successive elements do not satisfy the >>> predicate. >>> > rollingGroupBy :: (a -> a -> Bool) -> [a] -> [[a]] >>> > rollingGroupBy _ [] = [] >>> > rollingGroupBy cmp xs = >>> > let (ys, zs) = rollingSpan cmp xs >>> > in ys : rollingGroupBy cmp zs >>> > >>> > Are there any existing functions that serve this purpose or is there >>> any >>> > simpler way to achieve such functionality? If not, where is the right >>> place >>> > for these, if any. Can they be included in Data.List in base? >>> > >>> > Thanks, >>> > Harendra >>> > >>> > _______________________________________________ >>> > ghc-devs mailing list >>> > ghc-devs@haskell.org >>> > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >>> > >>> >> >> >> _______________________________________________ >> ghc-devs mailing list >> ghc-devs@haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >> >> > > > -- > brandon s allbery kf8nh sine nomine > associates > allber...@gmail.com > ballb...@sinenomine.net > unix, openafs, kerberos, infrastructure, xmonad > http://sinenomine.net >
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