protected internal virtual void PostWalk(UnboundExpression node) { }
 protected internal virtual void PostWalk(UnboundExpression node)
 {
 }
 // UnboundExpression
 protected internal virtual bool Walk(UnboundExpression node) { return true; }
 // UnboundExpression
 protected internal virtual bool Walk(UnboundExpression node)
 {
     return(true);
 }