Thanks. `mplus` is the glue I was looking for. The original algorithm
has a bug. Following is what I have for now:
searchTree pred rootLoc
| pred (getLabel rootLoc) = Just rootLoc
| otherwise = (right rootLoc >>= searchTree pred)
`mplus` (firstChild rootLoc >>= searchTree pred)
Jian
MightyByte <mightyb...@gmail.com> wrote:
> I haven't tested it, but I think you're looking for something like this:
>
> searchTree2 :: (a -> Bool) -> TreeLoc a -> Maybe (TreeLoc a)
> searchTree2 pred rootLoc =
> if pred (getLabel rootLoc)
> then Just rootLoc
> else firstChild rootLoc >>= siblings
> where siblings loc = searchTree2 pred loc `mplus`
> (searchTree2 pred =<< right loc)
>
>
> On Mon, Mar 8, 2010 at 1:11 PM, Jian Fan <abe...@gmail.com> wrote:
>> Hi,
>>
>> There doesn't seem to be a function to search the tree so
>> I come up with following function:
>>
>> searchTree :: (a -> Bool) -> TreeLoc a -> Maybe (TreeLoc a)
>> searchTree pred rootLoc =
>> if pred (getLabel rootLoc) then
>> Just rootLoc
>> else case firstChild rootLoc of
>> Just loc -> case searchTree pred loc of
>> Just loc -> Just loc
>> Nothing -> case right loc of
>> Just rLoc -> searchTree pred rLoc
>> Nothing -> Nothing
>> Nothing -> Nothing
>>
>> Which feels quite ugly. Any suggestions? Thanks.
>>
>> Jian
>>
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>> Haskell-Cafe@haskell.org
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>>
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