Haskell draw function arguments from two lists

Question

I'm trying to implement a kind of zip-function for trees. For this example each tree-node has an Integer Value (Label), a transformative function (Label->Label) and a List of sub-trees [Tree].

the tzp (tree-zip) Method takes two trees and adds their values together based on some criteria. Here's the question:

How do I get my function to recursively take the next subtree of each [Tree]-List?

My current implementation in case you're curious

tzp :: (Label -> Label -> Label) -> Tree -> Tree -> Tree
tzp arithmeticF t1 t2 = if ((getNodeValue t1) == (getNodeValue t2)) then (Node (arithmeticF (getNodeValue t1)) ((getNodeFunction t1) . (getNodeFunction t2) (getNodeValue t1)) (map (tzp arithmeticF) (getSubTrees t1) (getSubTrees t2)))

the culprit is this part:

(map (tzp arithmeticF) (getSubTrees t1) (getSubTrees t2))

since map can't work with two lists. To be precise I have to apply the function to the n'th element of either list. So first with first, second with second, etc.

Any help is greatly appreciated!

You need to post the definitions of the types you're working with. And you might be looking for zipWith? — bheklilr

utdemir utdemir · Accepted Answer · 2014-11-20T21:49:32

Prelude> :t uncurry
uncurry :: (a -> b -> c) -> (a, b) -> c
Prelude> :t (+)
(+) :: Num a => a -> a -> a
Prelude> :t uncurry (+)
uncurry (+) :: Num c => (c, c) -> c

So, something like:

map (uncurry tzp arithmeticF) (zip (getSubTrees t1) (getSubTrees t2))

Should do the trick.

Haskell draw function arguments from two lists

1 Answers