val http_pattern = """\"https?://[^\"]*\"""".r
def unquote(s: String) = s.drop(1).dropRight(1)
def get_all_URLs(page: String) : Set[String] = {
http_pattern.findAllIn(page).map(unquote).toSet
}
def crawl(url: String, n: Int) : Unit = {
if (n == 0) ()
else {
println(s"Visiting: $n $url")
for (u <- get_all_URLs(get_page(url)))
crawl(u, n - 1)
}
}