Re: [Haskell-beginners] list splitting - nice implementation?

On Sun, Nov 18, 2012 at 11:53:23AM +0100, Tobias Brandt wrote:

On 18 November 2012 11:33, Kim-Ee Yeoh wrote:

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On Sun, Nov 18, 2012 at 4:47 PM, Tobias Brandt wrote:

split xs = getSnds $ span (uncurry (<)) $ zip xs (tail xs)

...

where getSnds (as, bs) = (map snd as, map snd bs)

You could prepend negative infinity to not lose the first element.

Oops, didn't noticed that, nice catch. I'd rather do the following, as it works for all types that can be compared with (<), not just for numbers:

split xs = getSnds $ span (uncurry (<)) $ zip xs (tail xs) where getSnds (as, bs) = (head xs : map snd as, map snd bs)

ghci> split [] ([*** Exception: Prelude.head: empty list Better add a special case for split []. Incidentally, this is one splitting pattern (splitting based on a relation between consecutive elements) that the split package [1] does NOT cover. I think I have an idea of how to support it but it would require rewriting a bunch of the internals of the library. -Brent [1] http://hackage.haskell.org/package/split