/* event change; =>
   transient LinkedHashSet<Runnable> onChange;
   public selfType onChange(Runnable r) { onChange = syncAddOrCreate(onChange, r); this; }
   void change() { if (onChange != null) for (listener : onChange) pcallF_typed(listener); }
; }
*/
svoid tok_eventFunctions(LS tok) {
  int i;

  while ((i = jfind(tok, "event <id>", nIdx -> !eqGet(tok, nIdx+3, "aka"))) >= 0) {
    int iModifiers = tok_leftScanModifiers(tok, i);
    S modifiers = joinSubList(tok, iModifiers, i-1);
    int iSemicolon = i+4;
    LS tokArgs = null;
    if (eqGet(tok, i+4, "(")) {
      int argsFrom = i+6;
      int argsTo = findCodeTokens(tok, argsFrom, false, ")");
      tokArgs = subList(tok, argsFrom-1, argsTo);
      iSemicolon = argsTo+2;
    }

    int iEnd = iSemicolon+1;
    S body = "";
    if (eqGet(tok, iSemicolon, "{")) {
      iEnd = tok_findEndOfBlock(tok, iSemicolon);
      body = joinSubList(tok, iSemicolon+1, iEnd-1);
    } else if (neqGet(tok, iSemicolon, ";"))
      fail("Semicolon expected at end: " + joinSubList(tok, i, iSemicolon+1));
    
    S change = tok.get(i+2), prefix = "";
    if (startsWithCamelCaseWord(change, "on"))
      change = firstToLower(dropFirst(2, change));
    else if (startsWithCamelCaseWord(change, "fire")) {
      prefix = "fire";
      change = firstToLower(dropFirst(4, change));
    }
    S onChange = "on" + firstToUpper(change);
    S removeListener = "remove" + firstToUpper(change) + "Listener";
    
    LPairS args = tok_typesAndNamesOfParams(tokArgs);
    LS types = pairsA(args);
    S args1 = join(dropFirstAndLast(tokArgs));
    S args2 = joinWithComma(pairsB(args));
    S typeParams = joinWithComma(map tok_toNonPrimitiveTypes(types));      S listenerType = empty(args) ? "Runnable" : "IVF" + l(args) + "<" + typeParams + ">";
    S r = empty(args) ? "r" : "f";
    S fireChange = empty(prefix) ? change : prefix + firstToUpper(change);
   
    replaceTokens_reTok(tok, iModifiers, iEnd, 
      "\*modifiers*/ transient Set<\*listenerType*/> \*onChange*/;\n" +
      "public \*modifiers*/ selfType \*onChange*/(\*listenerType*/ \*r*/) { \*onChange*/ = createOrAddToSyncLinkedHashSet(\*onChange*/, \*r*/); this; }\n" +
      "public \*modifiers*/ selfType \*removeListener*/(\*listenerType*/ \*r*/) { main remove(\*onChange*/, \*r*/); this; }\n" +
      "public \*modifiers*/  void \*fireChange*/(\*args1*/) { \*body*/ " +
        "if (\*onChange*/ != null) for (listener : \*onChange*/) " +
        "pcallF_typed(" +
          joinNemptiesWithComma("listener", args2) + "); " +
      "}"
    );
  }
}

Began life as a copy of #1012742