Sample scala code for parsing user-defined expressions

ExpressionParser.scala

/*
Description: Parses expressions with two user-defined functions ("Max","Sum") and one operator ("+") acting upon three lists:
"l1", "l2", "l3"
Sample expression which can be parsed by this program:
Sum(Max(l1,l2),l3)+Max(l1,Sum(l1,l2)+l3)
To know more or to create your own parsers, visit:
http://www.artima.com/pins1ed/combinator-parsing.html
*/

import scala.util.parsing.combinator._

class ExpressionParser extends JavaTokenParsers {

  //Helper functions

  val m = Map("l1" -> List(1, 2, 3), "l2" -> List(2, 1, 4), "l3" -> List(5, 4, 1))

  def addColumns(x: List[Int], y: List[Int]): List[Int] = (x, y).zipped.map(_ + _)

  def maxColumns(x: List[Int], y: List[Int]): List[Int] = (x, y).zipped.map((a, b) => if (a > b) a else b)


  //Parsers

  def expr: Parser[List[Int]] =
    sum ^^ { case x => (List.fill(3)(0) /: x) ((a, b) => addColumns(a, b)) }


  def term: Parser[List[Int]] =
    "Sum(" ~> comma <~ ")" ^^ { case x => (List.fill(3)(0) /: x) ((a, b) => addColumns(a, b)) } |
      "Max(" ~> comma <~ ")" ^^ { case x => (List.fill(3)(0) /: x) ((a, b) => maxColumns(a, b)) } |
      identifier

  def comma: Parser[List[List[Int]]] = repsep(expr, ",")

  def sum: Parser[List[List[Int]]] = repsep(term, "+")

  def identifier: Parser[List[Int]] = ident ^^ {
    m(_)
  }

}


object MyParser extends ExpressionParser {

  def calculator(expr: Parser[Any], input: String) = {
    parseAll(expr, input) match {
      case Success(result, _) => Some(result)
      case NoSuccess(_, _) => None
    }
  }

  def main(args: Array[String]) {
    while (true) {
      val input = scala.io.StdIn.readLine()
      println(calculator(expr, input).get)
    }
  }
}