// returns true if it fired
static bool applyRule_first(S ruleID) {
  // process the rule
  Lisp rule = getLispTruth(ruleID);
  if (rule == null) { print("Rule not found: " + ruleID); false; }
  //print("Applying rule " + ruleID);
  print_setPrefixForThread(ruleID + "> ");
  try {
    ret applyRule_first(rule, ruleID);
  } finally {
    print_setPrefixForThread("");
  }
}

// ruleID is just as an info parameter to emit()
static bool applyRule_first(Lisp rule, S ruleID) {
  L<Lisp> conditions = dropLast(rule.args);
  Lisp out = last(rule.args);

  L<Map<S, Lisp>> results = matchConditions_all(conditions, new HashMap); // can be optimized
  //print("Got " + n(results, "results"));
  if (empty(results)) false;
  Map<S, Lisp> matches = first(results);
  //print("Yo! " + struct(matches));
  out = lispReplaceVars(out, matches);
  //print("Possibly defining: " + lispToEnglish_prettier(out));
  emit(out, ruleID);
  true;
}

Began life as a copy of #1008134