### Question:
GrammarSugar { public static NonTerminal optional(Symbol symbol) { Grammar g = symbol.getGrammar(); NonTerminal opt = g.newNonTerminal(g.uniqueName("opt_")); g.newRule(opt); g.newRule(opt, symbol); return opt; }  static NonTerminal seq(Symbol... symbols); static NonTerminal optional(Symbol symbol); static NonTerminal plus(Symbol symbol); static NonTerminal star(Symbol symbol); static NonTerminal star(Symbol symbol, StarRulesUpdater updater); static NonTerminal oneOf(Symbol first, Symbol... symbols); static NonTerminal oneOf(OneOfRuleUpdater updater, Symbol first, Symbol... symbols); static NonTerminal separated(Symbol item, Symbol separator); static NonTerminal separated(Symbol item, Symbol separator, boolean atLeastOne); static NonTerminal terminated(Symbol item, Symbol separator); static NonTerminal terminated(Symbol item, Symbol separator, boolean trailingOptional); static NonTerminal terminated(Symbol item, Symbol separator, boolean trailingOptional, boolean emptyStart); static NonTerminal terminated(Symbol item, Symbol separator, Symbol terminator, boolean trailingOptional, boolean emptyStart);  }### Answer:
@Test public void optionalPart() { Grammar g = new Grammar(); Terminal id = g.newTerminal("id"); Terminal error = g.newTerminal("error"); g.newRule(g.getStart(), optional(id)); LRParser parser = new LRParser(new SLRTableGenerator(g).generateTable()); assertEquals("[id]", "" + parser.parse(asLexemes(id))); assertEquals("[]", "" + parser.parse(asLexemes())); assertFalse(parser.parse(error)); }