On Thu, 4 Jun 2009, Paul Keir wrote:
Hi all,
If I have a list, and I'd like to convert it to a list of lists,
each of length n, I can use a function like bunch:
bunch _ [] = []
bunch n as = let (c,cs) = splitAt n as in c:bunch n cs
http://hackage.haskell.org/packages/archive/utility-ht/0.0.5.1/doc/html/Data-List-HT.html#v%3AsliceVertical
> bunch 8 [1..16]
[[1,2,3,4,5,6,7,8],[9,10,11,12,13,14,15,16]]
If I now want to do the same for the nested lists, I can compose
an application involving both map and bunch:
> map (bunch 4) . bunch 8 $ [1..16]
[[[1,2,3,4],[5,6,7,8]],[[9,10,11,12],[13,14,15,16]]]
and I can "bunch" the new length 4 lists again:
> map (map (bunch 2)) . map (bunch 4) . bunch 8 $ [1..16]
[[[[1,2],[3,4]],[[5,6],[7,8]]],[[[9,10],[11,12]],[[13,14],[15,16]]]]
Don't you first break the list into 2-element lists, then the resulting
list into 2-element lists and so on? I.e.
bunch 2 . bunch 2 . bunch 2 $ [1..16]
Calling 'bunch' multiple times is problematic since every call has a
different signature, a different depth of list nesting. I guess you have
to use a tree type, which allows arbitrary list nesting at run-time.
_______________________________________________
Haskell-Cafe mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/haskell-cafe
