val http_pattern = """"https?://[^"]*"""".r

val email_pattern = 

  """([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})""".r

def print_str(s: String) = 

  if (s == "") () else println(s)

def crawl(url: String, n: Int) : Unit = {

  if (n == 0) ()

  else {

    println(s"Visiting: $n $url")

    val page = get_page(url)

    print_str(email_pattern.findAllIn(page).mkString("\n"))

    for (u <- get_all_URLs(page).par) crawl(u, n - 1)

  }

}