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

[minh thu]

2009/2/10 minh thu <noteed at gmail.com>:
> 2009/2/10 Joachim Breitner <mail at joachim-breitner.de>:
>> Hi,
>>
>> Am Montag, den 09.02.2009, 16:41 -0700 schrieb Luke Palmer:
>>> 2009/2/9 Joachim Breitner <mail at joachim-breitner.de>
>>>         Now while this works, and while ST is still somewhat pure, I'm
>>>         wondering
>>>         if there is no better way of expressing "This piece of
>>>         information came
>>>         from the point in a data structure, so something else can be
>>>         put here
>>>         easily".
>>>
>>> You might want to look into zippers:
>>> http://haskell.org/haskellwiki/Zipper
>>
>> I thought about Zippers, but I understand that they improve _navigating_
>> in a Tree-like structure, or to refrence _one_ position in a tree.
>>
>> But if I would deconstruct my tree to the list of _all_ locations, with
>>> type Loc a = (Tree a, Cxt a)
>> and then run my algorithm that returns [(Loc a, Info)], it's still not
>> clear to me how I can combine all of these locations to get back my
>> original Tree, annotated with the Info returned.
>
> I guess I just repeat your last praragraph of your original mail but it seems
> to me you can mapAccump some 'names' on the tree, process an
> association list (or an IntMap) of the (name,log) then map the three
> again using the result.
> In spirits, it's the same thing than the STRef solution but it seems
> cleaner to me.

I forgot to mention you can try to tie the knot too, using the result
of the processing in the first mapping (and then you don't need the
second one)...