Tom Moertel's tree traversal ported from Haskell to Coffeescript.

traversal.coffee

# Translation of Tom Moertel's tree traversal:
#
# http://blog.moertel.com/posts/2012-01-26-the-inner-beauty-of-tree-traversals.html

t0 = []
t1 = [1]
t3 = [2, [1], [3]]

preorder_traversal = (f, z, tree) ->
  do go = (tree, z) ->
    return z unless tree?
    [v, l, r] = tree
    z1 = f(v, z)
    z2 = go(l, z1)
    z3 = go(r, z2)

inorder_traversal = (f, z, tree) ->
  do go = (tree, z) ->
    return z unless tree?
    [v, l, r] = tree
    z1 = go(l, z)
    z2 = f(v, z1)
    z3 = go(r, z2)

flatten = (traversal, tree) ->
  append = (i, a) -> a.concat(i)
  traversal append, [], tree

console.log flatten inorder_traversal, t3
console.log flatten preorder_traversal, t3

curry = (f, a) -> (x) -> f(a, x)
traverse = (step, f, z, tree) ->
  do go = (tree, z) ->
    return z unless tree?
    [v, l, r] = tree
    step curry(f, v), curry(go, l), curry(go, r), z

preorder  = (f, z, tree) -> traverse(((n, l, r, x) -> r l n x), f, z, tree)
inorder   = (f, z, tree) -> traverse(((n, l, r, x) -> r n l x), f, z, tree)
postorder = (f, z, tree) -> traverse(((n, l, r, x) -> n r l x), f, z, tree)

console.log flatten preorder, t3
console.log flatten inorder, t3
console.log flatten postorder, t3

leftorder  = (f, z, tree) -> traverse(((n, l, r, x) -> l n x), f, z, tree)
rightorder = (f, z, tree) -> traverse(((n, l, r, x) -> r n x), f, z, tree)

treemin = (tree) -> leftorder Math.min, Number.MAX_VALUE, tree
treemax = (tree) -> rightorder Math.max, -Number.MAX_VALUE, tree

console.log treemin t3
console.log treemax t3

More on this here.