manifest { t_data = 0, t_left = 1, t_right = 2, sizeof_t = 3 }

let info = nil;

let coroutA = nil, coroutB = nil, coroutC = nil;

let scan(tptr) be
     // tptr is the pointer to the root node of the tree,
{ let ok;
  if ptr = nil then
    return;
  scan(tptr ! t_left);
  info := tptr ! t_data;
  resume(coroutA);
  scan(tptr ! t_right); }

let checker() be
{ while true do
  { let data1 = nil, data2 = nil;
    if alive(coroutB) then
    { resume(coroutB);
      data1 := info }
    if alive(coroutC) then
    { resume(coroutC);
      data2 := info }
    if data1<>data2 then
    { outs("They are different\n");
      return }
    unless data1 \/ data2 do
    { outs("They are the same\n");
      return } } }

let start() be
{ let tree1, tree2;
  // fill the two trees with data
  coroutA := create_coroutine(checker);
  coroutB := create_coroutine(scan, tree1);
  coroutC := create_coroutine(scan, tree2);
  resume(coroutA) }