contract LHSMatching =

  function from_some(Some(x)) = x

  function
    length : list('a) => int
    length([])      = 0
    length(_ :: xs) = 1 + length(xs)

  function
    append([], ys)      = ys
    append(x :: xs, ys) = x :: append(xs, ys)

  function local_match(xs : list('a)) =
    let null([])     = true
    let null(_ :: _) = false
    !null(xs)

  entrypoint main() =
    from_some(Some([0]))
      ++ append([length([true]), 2, 3], [4, 5, 6])
      ++ [7 | if (local_match([false]))]