LeftRecursion.scala

/**
  * This code doen't work in Scala 2.7.X.
  */
import scala.util.parsing.combinator._
import scala.util.parsing.input._

object LeftRecursion extends PackratParsers {
  type Elem = Char
  lazy val any = elem("", _  != CharSequenceReader.EofCh)
  lazy val P: PackratParser[Any] = A ~ not(any)
  lazy val A: PackratParser[Any] = A ~ 'a' | success(null)
  def main(args: Array[String]) {
    implicit def in(str: String) = 
      new PackratReader(new CharSequenceReader(str))
    println(P("")) // success
    println(P("aaa")) // success
    println(P("b")) // failure
  }
}