test1 = \arr -> arr[0] + arr[1]

test2 = \arr -> case arr of 
  [x, y] -> x + y
  [x] -> x
  [] -> 0
  [x, y : _] -> x + y

data Tree = One Number | Some [Tree]

test3 = \tree, sum -> case tree of
  One n -> n
  Some [n1, n2 : rest] -> test3(n1, sum) * 10 + test3(n2, sum) * 5 + sum(rest)