[Haskell-beginners] list splitting - nice implementation?
byorgey at seas.upenn.edu
Sun Nov 18 16:13:15 CET 2012
On Sun, Nov 18, 2012 at 11:53:23AM +0100, Tobias Brandt wrote:
> On 18 November 2012 11:33, Kim-Ee Yeoh <ky3 at atamo.com> wrote:
> > On Sun, Nov 18, 2012 at 4:47 PM, Tobias Brandt <tob.brandt at googlemail.com>
> > 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  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.
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