[Haskell-cafe] Painting logs to get a coloured tree

[Joachim Breitner]

Hi,

Am Dienstag, den 10.02.2009, 16:36 +0100 schrieb minh thu:
> So here some code, notice the process function which work on a list
> of data (drawn from the tree). As said above, it can make use of a [0..]
> list if the 'tags' or 'names' are needed for processing.
> 
> Is it applicable to your problem ?
> 
> --------------------------
> 
> module Log where
> 
> data Tree a = Bud | Branch a (Tree a) (Tree a) -- no length here
>   deriving Show
> 
> mapAcc f acc Bud = (acc, Bud)
> mapAcc f acc (Branch a l r) = (acc2, Branch a' l' r')
>   where (acc0,a') = f acc a
>         (acc1,l') = mapAcc f acc0 l
>         (acc2,r') = mapAcc f acc1 r
> 
> tree0 = Bud
> tree1 = Branch "a" Bud Bud
> tree2 = Branch "r" (Branch "s" Bud Bud) Bud
> tree3 = Branch "x" (Branch "y" tree1 tree2) Bud
> 
> process :: [String] -> [String]
> process l = zipWith (\a b -> a ++ show b) l [0..]
> 
> tie tree = tree'
>   where ((acc,q),tree') = mapAcc (\(acc,p) a -> ((acc + 1,a:p),r !!
> acc)) (0,[]) tree
>         r = process (reverse q)

thanks for your work. It doesn’t fit directly (if the process operation
reorders the elements of the list, it fails). But if I first number
them, and later sort them again, or use lookup instead of !!, it would
work. But the knot-tying (and thus the single traversal of the tree) is
a very neat idea.

Greetings,
Joachim



-- 
Joachim Breitner
  e-Mail: mail at joachim-breitner.de
  Homepage: http://www.joachim-breitner.de
  ICQ#: 74513189
  Jabber-ID: nomeata at joachim-breitner.de
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