Re: [Haskell-cafe] How to get all the paths of a tree

19 Sep 2005


      On Mon, Sep 19, 2005 at 12:52:47PM +0200, Rene de Visser wrote:
...
-- This function can effectively only be used bottom up, because the only  input
-- parameter to func comes from the call "(map (treeFold func))", i.e. the rest of
-- the tree. We can only tell when are are at a leaf ( [b] is empty ).
-- Add in the other tree fold here!
treeFold :: (a -> [b] -> b) -> Tree a -> b
treeFold func (Node header list) = func header (map (treeFold func) list)
You can define paths with treeFold in this way:

paths t =
    treeFold
        (\a fs p ->
            let p' = p ++ [a] in
            if null fs
                then [p']
                else concatMap ($ p') fs)
        t
        []

So treeFold can be used top-down :-)

Best regards
Tomasz

Re: [Haskell-cafe] How to get all the paths of a tree

Tomasz Zielonka