Scala example source code file (packrat1.scala)

This example Scala source code file (packrat1.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

app, app, hello, list, list, nosuccess, packratparser, packratparser, packratparsers, parseresult, standardtokenparsers, success, success, test

The Scala packrat1.scala source code

import scala.util.parsing.combinator._

import scala.util.parsing.combinator.syntactical.StandardTokenParsers
import scala.util.parsing.input._
import scala.util.parsing.syntax._

import scala.collection.mutable.HashMap

object Test extends App{
  import grammars._

  val head = phrase(term)

  println(extractResult(head(new lexical.Scanner("1"))))
  println(extractResult(head(new lexical.Scanner("1+2"))))
  println(extractResult(head(new lexical.Scanner("9-4"))))
  println(extractResult(head(new lexical.Scanner("9*9"))))
  println(extractResult(head(new lexical.Scanner("8/2"))))
  println(extractResult(head(new lexical.Scanner("4*9-0/7+9-8*1"))))
  println(extractResult(head(new lexical.Scanner("(1+2)*3"))))
}

object grammars extends StandardTokenParsers with PackratParsers{
  
  def extractResult(r : ParseResult[_]) = r match {
    case Success(a,_) => a
    case NoSuccess(a,_) => a
  }
  
  lexical.delimiters ++= List("+","-","*","/","(",")")
  lexical.reserved ++= List("Hello","World")
  
  /****
   * term = term + fact | term - fact | fact
   * fact = fact * num  | fact / num  | num
   */


 val term: PackratParser[Int] = (term~("+"~>fact) ^^ {case x~y => x+y}
           |term~("-"~>fact) ^^ {case x~y => x-y}
           |fact)
  
 val fact: PackratParser[Int] = (fact~("*"~>numericLit) ^^ {case x~y => x*y.toInt}
           |fact~("/"~>numericLit) ^^ {case x~y => x/y.toInt}
           |"("~>term<~")"
           |numericLit ^^ {_.toInt})
 }