Class X Takes Types Parameters

Question

Reading through this informative, well-written article on Parser Combinators, I see this code:

class DisParser[+A](left: Parser[A], right: Parser[A]) extends Parser[A] {
  def apply(s: Stream[Character]) = left(s) match {
    case res: Success => res
    case _: Failure => right(s)
  }
}

When I try to compile this code, I get:

Parser.scala:19: error: class Success takes type parameters
    case res: Success => res
              ^
one error found

Given the signature of Parser:

case class Success[+A](value: A, rem: Stream[Character]) extends Result[A]

How can I change the case res: Success => res line to give Success a proper type parameter?

Answer 1

Which Success are you using? This one (Success from Parsers package) or this one (Success from util)? Both take type parameters, so you'll need to put it as

res @ Success(_, _) =>

otherwise you'll have to deal with the erasure warning.