Scala example source code file (ListParser.scala)

This example Scala source code file (ListParser.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

array, char, id, int, int, list, lst, lst, num, num, parsers, string, tree, tree

The Scala ListParser.scala source code

package examples.parsing

import scala.util.parsing.combinator.{Parsers, ImplicitConversions, ~, mkTilde}
import scala.util.parsing.input.CharArrayReader

object listParser {
  abstract class Tree
  case class Id(s: String)          extends Tree
  case class Num(n: Int)            extends Tree
  case class Lst(elems: List[Tree]) extends Tree

  import Character.{isLetter, isLetterOrDigit, isDigit}
  def mkString(cs: List[Any]) = cs.mkString("")

  class ListParsers extends Parsers {
    type Elem = Char
    
    lazy val ident = rep1(elem("letter", isLetter), elem("letter or digit", isLetterOrDigit)) ^^ {cs => Id(mkString(cs))}
    lazy val number = chainl1(elem("digit", isDigit) ^^ (_ - '0'), success{(accum: Int, d: Int) => accum * 10 + d}) ^^ Num
    lazy val list = '(' ~> repsep(expr, ',') <~ ')' ^^ Lst
    lazy val expr: Parser[Tree] = list | ident | number
  }

  def main(args: Array[String]) {
    println(
      if (args.length == 1) {
        (new ListParsers).expr(new CharArrayReader(args(0).toCharArray()))
      }
      else
        "usage: scala examples.parsing.listParser <list-string>"
    )
  }
}