[Haskell-cafe] are some of these "reverse" algos better than
others? is there a quick and dirty way to reveal this fact?
lennart at augustsson.net
Sun Sep 23 14:23:25 EDT 2007
Well, my goal when I first wrote it was to see if I could write reverse
without calling any other functions.
I did realize that it was really bad. :)
On 9/23/07, Felipe Almeida Lessa <felipe.lessa at gmail.com> wrote:
> On 9/23/07, Lennart Augustsson <lennart at augustsson.net> wrote:
> > If we're discussing bad versions of reverse, don't forget this one:
> > rev  = 
> > rev (x:xs) =
> > case rev xs of
> >  -> [x]
> > y:ys -> y : rev (x : rev ys)
> > It's different from most versions of reverse because it doesn't use any
> > auxiliarry functions.
> > It's also extremely inefficient.
> Wow! I'm amazed, this function runs in exponential time! How does one
> actually comes to write it without smelling something wrong with those
> recursive calls?
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