'Doing a binary tree'? You mean visiting every node? define walk-tree (tree fn &optional remaining-branches) match tree (Leaf l) -> funcall

'Doing a binary tree'? You mean visiting every node? define walk-tree (tree fn &optional remaining-branches) match tree (Leaf l) -> funcall fn l if remaining-branches walk-tree (first remaining-branches) fn (rest remaining-branches) (Tree t r l) -> funcall fn t walk-tree r fn (push l remaining-branches)