/* Mapping Visitor (Generic Version)
   A second-level framework, a part of the Binary Tree Traversal Framework
   H. Conrad Cunningham
   Version #1: 29 April 2010

This is a second-level framework that introduces a Mapping Visitor
that is a specialization and extension of the BinTreeVisitor feature
of the top-level framework.  

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*/


 /* Class MappingVisitor is a concrete binary tree visitor class that
    implements a map operation over BinTree's.  That is, it applies a
    unary operator to every value stored in the tree. This has the
    ConcreteVisitor role in the Visitor design pattern.  It also has
    the role Context in the Strategy design pattern.  Method visit is
    a template method for the Mapping Visitor second-level
    framework.

   Because the BinTree is mutated by
*/

class MappingVisitor[Val](op: Val => Val) extends BinTreeVisitor[Val] {

  // attributes
  private var vop = op

  // mutators
  def setMapOp(op: Val => Val) { vop = op }

  // visitor hook implementations
  def visit(t: Node[Val]) {
    t.setValue(vop.apply(t.getValue))
    val l = t.getLeft
    if (l != null) l.accept(this)
    val r = t.getRight
    if (r != null) r.accept(this)
  }

  def visit(t: NilTree[Val]) { }
}