resource Stack
  type result = enum(OK, OVERFLOW, UNDERFLOW)
  op push(item: int) returns r: result
  op pop(res item: int) returns r: result
body Stack(size: int)
  var store[1:size]: int, top: int := 0
  proc push(item) returns r
    if top<size -> store[++top] := item; r := OK
    [] top=size -> r := OVERFLOW
    fi
  end
  proc pop(item) returns r
    if top>0 -> item := store[top--]; r := OK
    [] top=0 -> r := UNDERFLOW
    fi
  end
end Stack

resource Stack_User()
  import Stack
  var x: Stack.result
  var s1, s2: cap Stack
  var y: int
  s1 := create Stack(10)
  vmcap := create vm() on <nomeMaquina>
  s2 := create Stack(20) on vmcap
   ...
  s1.push(4); s1.push(37); s2.push(98)
   ...
  if (x := s2.pop(y)) != OK -> ... fi
   ...
end