successor of x in c = the smallest element of c that is larger than x
min {y | y in c . y > x}
predecessor of x in c = the largest element of c that is smaller than x
max {y | y in c . y < x}
On Thu, 20 Apr 2023 at 21:08, Steffen Märcker <merk...@web.de> wrote:
> Dear Richard,
>
> thanks for that additional piece. I'll put insert-<left/right> on my list
> of possible variants. I think we come back to naming after the initial port
> is done and everyone can play with it. Generally, I made the observation to
> better be careful with names since it's too easy to alienate other or
> trigger wrong assumptions.
>
> New topic! (quote below)
>
> Honestly, my knowledge of Haskell is rather limited and rusted. Hence, I
> am having difficulties understanding what exactly these operations with a
> sequence of elements. Can you give an example or some pseude/smalltalk code
> from your use-case and library?
>
> Kind regards
>
>
> Changing the subject a wee bit, there's an operation family
> in my library, and I wonder how it would fit into Transducers?
> To avoid bias, here's a specification in Haskell (for lists,
> because I haven't had any luck installing Data.Witherable).
>
> uccessorBy, predecessorBy :: (a -> a -> Ordering) -> a -> [a] -> a
> successor, predecessor :: Ord a => a -> [a] -> a
>
> successor = successorBy compare
>
> successorBy cmp x = minimumBy cmp . filter (\y -> cmp x y == LT)
>
> predecessor = predecessorBy compare
>
> predecessorBy cmp = successorBy (flip cmp)
>
> The reason these operations exist is to pick neighbouring
> elements in SortedCollections and SortedSets. But they make
> *sense* for any Enumerable. So there are "generic"
> definitions with orderrides for those two classes.
>
> A filter + a reduce . Traditionally, a #select:thenFold:ifNone:
> in order to avoid building an intermediate collection. That much
> I see how to do with transducers. But you can't get the desired
> override for #successor:[sortBlock:][ifNone:] by overriding
> #select:thenFold:ifNone: in SortedCollection or SortedSet. So what
> *should* one do?
>
>
