[Haskell-cafe] Re: search Data.Tree.Zipper

8 Mar 2010


      I somehow cannot figure this out. Tree is Foldable so I
can use "find" on it. But how can I use find on TreeLoc?
Am I missing something obvious?

Dan Weston  wrote:
...
I think you want
find :: Foldable t => (a -> Bool) -> t a -> Maybe a
Jian Fan 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
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe