[Haskell-cafe] version sorting?

[MarLinn]

> versionSort :: [String] -> [String]
> versionSort = sortOn brkND
>   where
>     tr f g (x,y) = f x : g y
>     -- ND for non-digits
>     brkND = tr Right brkD . span (not . isDigit)
>     brkD = tr (Left . read @Int) brkND . span isDigit
>
> (side question: does the helper function tr I defined above have a
> commonly known name?)

I don't think so, but that's just because you made the cut at a weird
point. It's very close to (***)
<https://hoogle.haskell.org/?hoogle=%28***%29&scope=set%3Astackage> from
Control.Arrow, Data.Tuple.Extra, Data.Profunctor, and other libraries,
also known as bimap
<https://hoogle.haskell.org/?hoogle=bimap&scope=set%3Astackage> in
Data.Bifunctor and in the lens package.

Rewriting your functions to tease it out even more (not tested):

    versionSort :: [String] -> [String]
    versionSort = sortOn gatherNonDigits
      where

        gatherAll predicate gather continue = uncurry (:) . (gather *** continue) . span predicate

        -- 'NonDigits' for non-digits
        gatherNonDigits = gatherAll (not . isDigit) wrapNonDigits gatherDigits
        gatherDigits    = gatherAll        isDigit  wrapDigits    gatherNonDigits

        wrapNonDigits   = Right
        wrapDigits      = Left . read @Int


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