trees.sml

datatype fruit =
    Peach
  | Apple
  | Pear
  | Lemon
  | Fig

  datatype tree =
      Bud
    | Flat of fruit * tree
    | Split of tree * tree

(* height : tree -> int *)
fun height Bud = 0
  | height (Flat(_,  t)) = 1 + height (t)
  | height (Split(s, t)) = 1 + Int.max (height(s), height(t))

val smol_tree = Split (Bud, Flat (Peach, Bud))
val larger_tree = Split (Flat (Apple, Flat (Lemon, Bud)), Flat (Peach, Bud))

val smol_height = height smol_tree
val larger_height = height larger_tree