scope test_PStack

/* Goal: Allow probabilistic branching deep within nested function calls

  Like this, to return 4 different values:

  S color = "black" with probability 0.75
    or "white" with probability 0.25;
  S shape = "circle" with probability 0.4
    or "square" with probability 0.6;
  return "A " + color + " " + shape;
*/

sclass #C1 extends PStackComputableWithStep<S> {
  S color;

  public void step(IPStack stack) {
    if (step == 0) {
      ++step;
      stack.options(this, ll(
        o -> o.color = "red",
        o -> o.color = "green"));
    } else
      stack.ret(color);
  }
}

please include function test_BStack.

svoid test_PStack() {
  test_PStack_oneBranch();
  test_PStack_twoBranches();
  test_PStack_oneBranch3Options();
  test_PStack_twoBranches3Options();
  test_PStack_noOptions();
}

svoid test_PStack_oneBranch() {
  assertEqualsVerbose(
    ll("Color is black", "Color is white"),
    pstackComputeAll(new test_BStack_OneBranch));
}

svoid test_PStack_oneBranch3Options() {
  assertEqualsVerbose(
    ll("Color is black", "Color is white", "Color is gray"),
    pstackComputeAll(new test_BStack_OneBranch3Options));
}

svoid test_PStack_twoBranches() {
  assertEqualsVerbose(
    ll("A black circle", "A black square",
      "A white circle", "A white square"),
    pstackComputeAll(new test_BStack_TwoBranches));
}

svoid test_PStack_twoBranches3Options() {
  assertEqualsVerbose(
    ll("A black circle", "A black square", "A black triangle",
      "A white circle", "A white square", "A white triangle",
      "A gray circle", "A gray square", "A gray triangle"),
    pstackComputeAll(new test_BStack_TwoBranches3Options));
}

svoid test_PStack_noOptions() {
  assertInnerExceptionOfTypeVerbose(PStack.NoOptionsException.class,
    -> pstackComputeAll(new test_BStack_NoOptions));
}

Began life as a copy of #1035397