type FetchPage = String => String
type FindImages = String => List[String]

object WillFetchPage extends FetchPage {
    def apply(url:String):String = /* get content of the url */
}

class WillFindImages(fetchPage: FetchPage) extends FindImages {
    def apply(url:String):List[String] = {
       val html = fetchPage(url)
       // get image srcs from the <img> tags
    }
}

val findImages = new WillFindImages(WillFetchPage)

val testFindImages = new WillFindImages(_ => "html-have-3-images")
val images = testFindImages("any-url")
// assertion

sealed trait KiloGram

def KiloGram[A](a: A): A @@ KiloGram = Tag[A, KiloGram](a)

val mass = KiloGram(20.0)

2 * mass

object FetchPage extends ((String => Try[String]) @@ FetchType)

Error:(18, 51) class type required but String => scala.util.Try[String] with
    scalaz.Tagged[object_as_func.FetchType] found
object FetchPage extends ((String => Try[String]) @@ FetchType) {
                                                  ^