get "libhdr"
manifest $(
    VAL=0
    LEFT=1
    RIGHT=2
$)

let tree(v,l,r) = valof
$(  let obj = getvec(2)
    obj!VAL := v
    obj!LEFT := l
    obj!RIGHT := r
    resultis obj
$)

let preorder(tree, cb) be unless tree=0
$(  cb(tree!VAL)
    preorder(tree!LEFT, cb)
    preorder(tree!RIGHT, cb)
$)

let inorder(tree, cb) be unless tree=0
$(  inorder(tree!LEFT, cb)
    cb(tree!VAL)
    inorder(tree!RIGHT, cb)
$)

let postorder(tree, cb) be unless tree=0
$(  postorder(tree!LEFT, cb)
    postorder(tree!RIGHT, cb)
    cb(tree!VAL)
$)

let levelorder(tree, cb) be
$(  let q=vec 255
    let s=0 and e=1
    q!0 := tree
    until s=e do
    $(  unless q!s=0 do
        $(  q!e     := q!s!LEFT
            q!(e+1) := q!s!RIGHT
            e       := e+2
            cb(q!s!VAL)
        $)
        s := s+1
    $)
$)

let traverse(name, order, tree) be
$(  let cb(n) be writef("%N ", n)
    writef("%S:*T", name)
    order(tree, cb)
    wrch('*N')
$)

let start() be
$(  let example = tree(1, tree(2, tree(4, tree(7, 0, 0), 0),
                                  tree(5, 0, 0)),
                          tree(3, tree(6, tree(8, 0, 0),
                                          tree(9, 0, 0)),
                                  0))
    traverse("preorder", preorder, example)
    traverse("inorder", inorder, example)
    traverse("postorder", postorder, example)
    traverse("level-order", levelorder, example)
$)