parser combinator in Scala that parses floats

FloatParser.scala

import scala.util.parsing.combinator.JavaTokenParsers

trait FloatParser {

  private object parsers extends JavaTokenParsers {

    implicit class RichElem[A <% Parser[A]](p: A) {
      def <::>(q: Parser[List[A]]) = p ~ q ^^ { case m ~ n => m :: n }
    }

    implicit class RichListElem[A](p: Parser[List[A]]) {
      def <++>(q: Parser[List[A]]) = p ~ q ^^ { case m ~ n => m ::: n }
    }

    implicit class RichParser[A](p: Parser[A]) {
      def <::>[B <: A](q: Parser[List[B]]) = p ~ q ^^ { case m ~ n => m :: n }
    }

    lazy val digit = elem("digit", '0' to '9' contains _)
    lazy val number = rep1(digit)
    lazy val plus = '+' ~> number
    lazy val minus = '-' <::> number
    lazy val integer = plus | minus | number

    lazy val decimal = '.' <::> number | success(Nil)

    lazy val exponent = (elem('e') | elem('E')) <::> integer | success(Nil)

    lazy val float = integer <++> decimal <++> exponent ^^ (_.mkString)
  }

  def parseFloat(in: String): Double = {
    import parsers._
    parseAll(float, in) match {
      case Success(s, _) => s.toDouble
      case NoSuccess(m, _) => sys.error(m)
    }
  }
}

object Test extends App with FloatParser {
  println(parseFloat("1.2E-3"))
}