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package examples.parsing
import scala.util.parsing.combinator.{Parsers, ImplicitConversions, ~, mkTilde}
import scala.util.parsing.input.CharArrayReader
object listParser {
abstract class Tree
case class Id(s: String) extends Tree
case class Num(n: Int) extends Tree
case class Lst(elems: List[Tree]) extends Tree
import Character.{isLetter, isLetterOrDigit, isDigit}
def mkString(cs: List[Any]) = cs.mkString("")
class ListParsers extends Parsers {
type Elem = Char
lazy val ident = rep1(elem("letter", isLetter), elem("letter or digit", isLetterOrDigit)) ^^ {cs => Id(mkString(cs))}
lazy val number = chainl1(elem("digit", isDigit) ^^ (_ - '0'), success{(accum: Int, d: Int) => accum * 10 + d}) ^^ Num
lazy val list = '(' ~> repsep(expr, ',') <~ ')' ^^ Lst
lazy val expr: Parser[Tree] = list | ident | number
}
def main(args: Array[String]) {
println(
if (args.length == 1) {
(new ListParsers).expr(new CharArrayReader(args(0).toCharArray()))
}
else
"usage: scala examples.parsing.listParser <list-string>"
)
}
}
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