ScalaRunTimeForScalaJS.scala

object ScalaRunTimeForScalaJS {
  def main(a: Array[String]): Unit = {
    println(replStringOf((1 to 200).toList, 10))
  }
  
  def replStringOf(arg: Any, maxElements: Int): String =
    stringOf(arg, maxElements) match {
      case null => "null toString"
      case s if s.indexOf('\n') >= 0 => "\n" + s + "\n"
      case s => s + "\n"
    }

  def stringOf(arg: Any, maxElements: Int): String = {
    def isScalaClass(x: AnyRef)         = x.getClass.getName startsWith "scala."

    def isTuple(x: Any) = x != null && x.getClass.getName.startsWith("scala.Tuple")

    type AnyConstr[X] = Any

    def useOwnToString(x: Any) = x match {
      case _: Range | _: collection.immutable.NumericRange[_] => true
      case _: collection.SortedOps[_, _]  => true
      case _: collection.StringView | _: collection.StringOps | _: collection.mutable.StringBuilder => true
      case _: collection.View[_] => true
      case x: Iterable[_] => (!x.isInstanceOf[collection.StrictOptimizedIterableOps[_, AnyConstr, _]]) || !isScalaClass(x)
      case _ => false
    }

    def mapInner(arg: Any): String = arg match {
      case (k, v)   => inner(k) + " -> " + inner(v)
      case _        => inner(arg)
    }

    def arrayToString(x: AnyRef) = {
      if (x.getClass.getComponentType == classOf[runtime.BoxedUnit])
        (0 until math.min(java.lang.reflect.Array.getLength(x), maxElements)).map(_ => "()").mkString("Array(", ", ", ")")
      else
        x.asInstanceOf[Array[_]].iterator.take(maxElements).map(inner).mkString("Array(", ", ", ")")
    }

    def inner(arg: Any): String = arg match {
      case null                         => "null"
      case ""                           => "\"\""
      case x: String                    => if (x.head.isWhitespace || x.last.isWhitespace) "\"" + x + "\"" else x
      case x if useOwnToString(x)       => x.toString
      case x: AnyRef if x.getClass.isArray      => arrayToString(x)
      case x: Product1[_] if isTuple(x) => "(" + inner(x._1) + ",)" // that special trailing comma
      case x: Product if isTuple(x)     => x.productIterator.map(inner).mkString("(", ",", ")")
      case x                            => x.toString
    }

    inner(arg)
  }
}