Re: [Haskell-cafe] Re: Understanding tail recursion and trees

On Thu, May 1, 2008 at 9:32 AM, Edsko de Vries wrote:

So then the question becomes: what *is* the best way to write this function?

I guess it would be simpler to have the counter on the data type and a smart branch constructor:

data Tree = Leaf Integer | Branch Integer Tree Tree

count :: Tree -> Integer count (Leaf _) = 1 count (Branch c _ _) = c

branch :: Tree -> Tree -> Tree branch left right = Branch (count left + count right) left right

gentreeL :: Integer -> Tree gentreeL 0 = Leaf 0 gentreeL n = branch (gentreeL (n-1)) (Leaf 0)

etc. -- Felipe.