define process {
  // argument = xs
  0 // zeros
  0 // sum
  0 // i
  [
    dig3 // bring xs to top of local stack
    dupd swap get_at eqz // xs[i] == 0
      [[inc] dip3] // inc zeros
      []
    if
    dupd swap get_at // tmp = xs[i]
    [bury3] dip // put xs to bottom of local stack
    swap [add_int] dip // sum += tmp
    inc // ++i
  ]
  [
    dig3 count [bury3] dip dupd lt_int // i <= xs.Size
  ]
  while
  pop // remove i
  swap sub_int // sum-zeros
}