113 

   113 

   114 lazy val E: Parser = (T ~ T_OP("+") ~ E) || T  // start symbol

   114 lazy val E: Parser = (T ~ T_OP("+") ~ E) || T  // start symbol

   115 lazy val T: Parser = (F ~ T_OP("*") ~ T) || F

   115 lazy val T: Parser = (F ~ T_OP("*") ~ T) || F

   116 lazy val F: Parser = (T_LPAREN ~ E ~ T_RPAREN) || NumParser

   116 lazy val F: Parser = (T_LPAREN ~ E ~ T_RPAREN) || NumParser

   117    

   117    

   118 println(E.parse_all(tokenizer(lexing_rules, "1 + 2 + 3")))

   119 println(E.parse_all(tokenizer(lexing_rules, "1 + 2 + 3")))

   119 

   120 

   120 def eval(t: ParseTree) : Int = t match {

   121 def eval(t: ParseTree) : Int = t match {

   121   case Leaf(T_NUM(n)) => n.toInt

   122   case Leaf(T_NUM(n)) => n.toInt

   122   case Branch(List(t1, Leaf(T_OP("+")), t2)) => eval(t1) + eval(t2)

   123   case Branch(List(t1, Leaf(T_OP("+")), t2)) => eval(t1) + eval(t2)