Scala example source code file (ArithmeticParser.scala)

This example Scala source code file (ArithmeticParser.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, array, list, parser, parser, stdlexical, stdlexical, stdtokenparsers, tokens, tokens

The Scala ArithmeticParser.scala source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2006-2011, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |                                         **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package examples.parsing

import scala.util.parsing.combinator.lexical.StdLexical
import scala.util.parsing.combinator.syntactical.StdTokenParsers

/** Parse and evaluate a numeric expression as a sequence of terms, separated by + or -
 *   a term is a sequence of factors, separated by * or /
 *   a factor is a parenthesized expression or a number
 *
 * @author Adriaan Moors 
 */ 
object arithmeticParser extends StdTokenParsers {   
  type Tokens = StdLexical ; val lexical = new StdLexical
  lexical.delimiters ++= List("(", ")", "+", "-", "*", "/")

  lazy val expr =   term*("+" ^^^ {(x: int, y: int) => x + y} | "-" ^^^ {(x: int, y: int) => x - y})
  lazy val term = factor*("*" ^^^ {(x: int, y: int) => x * y} | "/" ^^^ {(x: int, y: int) => x / y})
  lazy val factor: Parser[int] = "(" ~> expr <~ ")" | numericLit ^^ (_.toInt)
  
  def main(args: Array[String]) {
    println(
      if (args.length == 1) {
        expr(new lexical.Scanner(args(0)))
      }
      else
        "usage: scala examples.parsing.arithmeticParser <expr-string>"
    )
  }
}


object arithmeticParserDesugared extends StdTokenParsers {   
  type Tokens = StdLexical ; val lexical = new StdLexical
  lexical.delimiters ++= List("(", ")", "+", "-", "*", "/")

  lazy val expr = chainl1(term, (keyword("+").^^^{(x: int, y: int) => x + y}).|(keyword("-").^^^{(x: int, y: int) => x - y}))
  lazy val term = chainl1(factor, (keyword("*").^^^{(x: int, y: int) => x * y}).|(keyword("/").^^^{(x: int, y: int) => x / y}))
  lazy val factor: Parser[int] = keyword("(").~>(expr.<~(keyword(")"))).|(numericLit.^^(x => x.toInt))   
  
  def main(args: Array[String]) {
    println(
      if (args.length == 1) {
        expr(new lexical.Scanner(args(0)))
      }
      else
        "usage: scala examples.parsing.arithmeticParser <expr-string>"
    )
  }
}