what's wrong with the var?

ExprParser

package ch19.sec02

import scala.util.parsing.combinator._

class ExprParser extends RegexParsers {
  val number = "[0-9]+".r
  def expr: Parser[Any] = term ~ opt("+" | "-") ~ expr
  def term: Parser[Any] = factor ~ rep("*" ~ factor)
  def factor: Parser[Any] = number | "(" ~ expr ~ ")"
}

object Main1 extends App {
  // here parser is define as var, can't compile
  var parser = new ExprParser
  val result = parser.parseAll(parser.expr, "3-4*5")
  if (result.successful) println(result.get)
}


object Main2 extends App {
  val parser = new ExprParser
  val result = parser.parseAll(parser.expr, "3-4*5")
  if (result.successful) println(result.get)
}