Skew K-ary tree

skew.u

-- Structure: a buffer of Arity, then a list of complete trees of exponentially increasing size
type Skew a = Skew [a] [(Nat, [Skew.Tree a])]
type Skew.Tree a = Tree [a] [Skew.Tree a] 

Skew.Arity = 4

Skew.cons : a -> Skew a -> Skew a
Skew.cons a = cases Skew hd spine ->  
  hd' = a +: hd
  if List.size hd' < Arity then Skew hd' spine 
  else match spine with 
    [] -> Skew [] [(Arity, [Tree hd' []])]
    (sz, forest) +: tl 
      | List.size forest == Arity -> 
        sz' = sz * Arity + Arity
        t = Tree hd' forest
        match tl with 
          (sz2, forest2) +: tl | sz2 == sz' -> 
            forest2' = t +: forest2
            Skew [] ((sz', forest2') List.+: tl)
          _ -> Skew [] ((sz', [t]) +: tl)
      | sz == Arity -> Skew [] ((sz, Tree hd' [] +: forest) +: tl)
      | otherwise -> Skew [] ((Arity, [Tree hd' []]) +: spine)

> List.foldRight Skew.cons (Skew [] []) (range 0 64)