HtmlDSL using Dynamic

htmldsl.scala

import scala.language.dynamics

import scala.util.DynamicVariable

sealed trait Node {
  def toXml: String
}

case class ElementNode(name: String, attributes: Map[String, String], children: List[Node]) extends Node {
  def toXml = {
    val as = attributes.mapValues("\"" + _ + "\"")
    s"""<${name}${as.map { case (l, r) => s" $l=$r" }.mkString}>${children.map(_.toXml).mkString}</${name}>"""
  }
}
case class TextNode(text: String) extends Node {
  def toXml = text
}

trait HtmlDSL {
  protected val nodes = new DynamicVariable[List[Node]](null)
  protected val attributes = new DynamicVariable[List[(String, String)]](null)

  object % extends Dynamic{
    def selectDynamic(name: String) = applyDynamic(name){}
    def applyDynamic(name: String)(body: => Unit): Unit = {
      val (ns, as) =
        nodes.withValue(List()) {
          attributes.withValue(List()) {
            body
            (nodes.value.reverse, attributes.value.toMap)
          }
        }
      nodes.value = ElementNode(name, as, ns) :: nodes.value
    }
  }

  def $(as: (String, String)*) = attributes.value = attributes.value ++ as

  def t(text: String) = nodes.value = TextNode(text) :: nodes.value

  def dsl(body: => Unit) = nodes.withValue(List()) {
    body
    nodes.value.head
  }
}

object Sample extends HtmlDSL {
  val html = dsl {
    %html {
      %head {
        %link($("rel" -> "stylesheet", "href" -> "style.css"))
        %title {
          t("タイトルだよ")
        }
      }
      %body {
        %p {
          t("本文だよ")
        }
      }
    }
  }

  def print = println(html.toXml)
}