scope test_BStack

/* Goal: Java code with backtracking, like this, to return 4 different values:

  S color = "black" or "white";
  S shape = "circle" or "square";
  return "A " + color + " " + shape;
*/

sclass #OneBranch extends VStackComputableWithStep<S> {
  S color, shape;

  void step(VStack stack) {
    cast stack to BStack;

    if (step == 0) {
      step = 1;
      stack.options(this,
        f -> f.color = "black",
        f -> f.color = "white");
    } else
      stack.return("Color is " + color);
  }
}}

svoid test_BStack() {
  assertListEqualsVerbose(
    ll("Color is black", "Color is white"),
    new BStackComputeAllWithPrintStruct(new OneBranch)!);
}