IvanVergiliev/tree_transform_dry.scala

## tree_transform_dry.scala
def transformTree(tree: Tree): Option[Tree] = {
  // Notice that there's no `canTranform` - we're using
  // `transform().isDefined` to check for transformability!
  val transformedLeft = if (transform(tree.left).isDefined) {
    transform(tree.left)
  } else None

  ...
}
	def transformTree(tree: Tree): Option[Tree] = {
	// Notice that there's no `canTranform` - we're using
	// `transform().isDefined` to check for transformability!
	val transformedLeft = if (transform(tree.left).isDefined) {
	transform(tree.left)
	} else None

	...
	}