Scala example source code file (Lexer.scala)

This example Scala source code file (Lexer.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

e, eof, eofch, eofch, errortoken, errortoken, invalid, invalid, list, numericlit, option, parser, parser, string

The Scala Lexer.scala source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2006-2011, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */



package scala.util.parsing.json

import scala.util.parsing.combinator._
import scala.util.parsing.combinator.syntactical._
import scala.util.parsing.combinator.lexical._
import scala.util.parsing.input.CharArrayReader.EofCh

/**
 *  @author Derek Chen-Becker <"java"+@+"chen-becker"+"."+"org">
 */
class Lexer extends StdLexical with ImplicitConversions {

  override def token: Parser[Token] =
    //( '\"' ~ rep(charSeq | letter) ~ '\"' ^^ lift(StringLit)
    ( string ^^ StringLit
    | number ~ letter ^^ { case n ~ l => ErrorToken("Invalid number format : " + n + l) }
    | '-' ~> whitespace ~ number ~ letter ^^ { case ws ~ num ~ l => ErrorToken("Invalid number format : -" + num + l) }
    | '-' ~> whitespace ~ number ^^ { case ws ~ num => NumericLit("-" + num) }
    | number ^^ NumericLit
    | EofCh ^^^ EOF
    | delim
    | '\"' ~> failure("Unterminated string")
    | rep(letter) ^^ checkKeyword
    | failure("Illegal character")
    )

  def checkKeyword(xs : List[Any]) = {
    val strRep = xs mkString ""
    if (reserved contains strRep) Keyword(strRep) else ErrorToken("Not a keyword: " + strRep)
  }

  /** A string is a collection of zero or more Unicode characters, wrapped in
   *  double quotes, using backslash escapes (cf. http://www.json.org/).
   */
  def string = '\"' ~> rep(charSeq | chrExcept('\"', '\n', EofCh)) <~ '\"' ^^ { _ mkString "" }

  override def whitespace = rep(whitespaceChar)

  def number = intPart ~ opt(fracPart) ~ opt(expPart) ^^ { case i ~ f ~ e =>
    i + optString(".", f) + optString("", e)
  }
  def intPart = zero | intList
  def intList = nonzero ~ rep(digit) ^^ {case x ~ y => (x :: y) mkString ""}
  def fracPart = '.' ~> rep(digit) ^^ { _ mkString "" }
  def expPart = exponent ~ opt(sign) ~ rep1(digit) ^^ { case e ~ s ~ d =>
    e + optString("", s) + d.mkString("")
  }

  private def optString[A](pre: String, a: Option[A]) = a match {
    case Some(x) => pre + x.toString
    case None => ""
  }

  def zero: Parser[String] = '0' ^^^ "0"
  def nonzero = elem("nonzero digit", d => d.isDigit && d != '0')
  def exponent = elem("exponent character", d => d == 'e' || d == 'E')
  def sign = elem("sign character", d => d == '-' || d == '+')

  def charSeq: Parser[String] =
    ('\\' ~ '\"' ^^^ "\""
    |'\\' ~ '\\' ^^^ "\\"
    |'\\' ~ '/'  ^^^ "/"
    |'\\' ~ 'b'  ^^^ "\b"
    |'\\' ~ 'f'  ^^^ "\f"
    |'\\' ~ 'n'  ^^^ "\n"
    |'\\' ~ 'r'  ^^^ "\r"
    |'\\' ~ 't'  ^^^ "\t"
    |'\\' ~> 'u' ~> unicodeBlock)

  val hexDigits = Set[Char]() ++ "0123456789abcdefABCDEF".toArray
  def hexDigit = elem("hex digit", hexDigits.contains(_))

  private def unicodeBlock = hexDigit ~ hexDigit ~ hexDigit ~ hexDigit ^^ {
    case a ~ b ~ c ~ d =>
      new String(Array(Integer.parseInt(List(a, b, c, d) mkString "", 16)), 0, 1)
  }

  //private def lift[T](f: String => T)(xs: List[Any]): T = f(xs mkString "")
}