[Haskell-cafe] Idiomatically using lists

[Dan Weston]

I would think a simple cyclic list should work without any copying at all:

rotateList myList n = take m . drop n $ x
   where x = myList ++ x
         m = length myList

Just keep dropping elements to rotate.

A possible alternative is to use a more tailored data structure with a 
zipper. See http://www.haskell.org/haskellwiki/Zipper

Dan

kevin birch wrote:
> Hello all,
> 
> I have an implementation question that I hope someone can help out 
> with.  Say I have a fixed-size list: [1, 2, 3, 4, 5] that I want to 
> treat as circular in a function in order to rotate one of the elements n 
> positions.  So rotating the second element 2 positions would result in: 
> [1, 3, 4, 2, 5], or rotating the fourth element 2 positions would result 
> in: [1, 2, 4, 3, 5].  There are two cases: if the element can be moved 
> w/o rotating and where the element must be inserted into the list at the 
> front.  Is there an idomatic way to handle both of these cases in a 
> function?
> 
> Thanks,
> kevin
> 
> 
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