build.sbt

scalaVersion := "2.11.7"

libraryDependencies += "com.github.scalaprops" %% "scalaprops-gen" % "0.1.13"
libraryDependencies += "com.typesafe.play" %% "play-netty-server" % "2.4.3"

Tree2SVG.scala

package scalaz

import java.io.{FileInputStream, File}
import java.nio.file.Files
import java.util.Collections.singletonList

import scalaprops.Gen
import scala.util.Random

object Tree2SVG {

  def main(args: Array[String]): Unit = {
    import play.core.server._
    import play.api.routing.sird._
    import play.api.mvc._

    val server = NettyServer.fromRouter(ServerConfig(
      mode = play.api.Mode.Test
    )) {
      case GET(p"/") => Action {
        Results.Ok(generateSVG()).as("image/svg+xml")
      }
    }
  }

  def generateSVG(): String = {
    val s = Stream.continually(Random.nextInt(128)).distinct
    val i = s.iterator
    def next(): Int = i.next
    val uniqueIntTreeGen = Gen.treeGen(Gen.gen((_, r) => (r, next())))
    val t = uniqueIntTreeGen.sample(seed = System.currentTimeMillis()).map(_.toString)
    val g = graph(Foldable[Tree].toList(t), treeEdges(t))
    val f = new File("tree.svg")
    toSVG(g, f)
    scala.io.Source.fromFile(f).getLines().mkString
  }

  def withTmpDir[T](action: File => T): T = {
    val dir = Files.createTempDirectory(System.currentTimeMillis().toString).toFile
    try {
      action(dir)
    }
    finally {
      dir.delete()
    }
  }

  def toSVG(graph: String, output: File): Unit = withTmpDir { dir =>
    import scala.sys.process._
    val name = System.currentTimeMillis.toString
    val dotFile = new File(dir, name + ".dot")
    Files.write(dotFile.toPath, singletonList(graph))
    // http://www.graphviz.org/
    Seq("dot", "-o" + output.getAbsolutePath, "-Tsvg", dotFile.getAbsolutePath).!
  }

  def treeEdges[A](tree: Tree[A]): List[(A, A)] = {
    def loop(s: Tree[A], parent: A): Stream[(A, A)] =
      s.subForest.flatMap{ sub =>
        loop(sub, sub.rootLabel) ++ List(parent -> sub.rootLabel)
      }
    loop(tree, tree.rootLabel).toList
  }

  val quote = "\"" + (_: String) + "\""

  def graph(nodes: List[String], edges: List[(String, String)]): String = s"""
digraph "tree" {
  node [
  ]
  edge [
  ]

  ${nodes.iterator.map(quote).mkString("\n")}

  ${edges.iterator.map{case (a, b) => quote(a) + " -> " + quote(b)}.mkString("\n")}
}
"""

}