// Default costructor, inits values
 public IfStatementASTNode()
     : base(ASTNodeType.ASTTYPE_IFSTATEMENT)
 {
     expr  = null;
     block = null;
 }
 // Set constructor.
 public IfStatementASTNode(ExprASTNode expr, BlockASTNode block)
     : this()
 {
     this.expr  = expr;
     this.block = block;
 }
 // Default costructor, inits values
 public WhileStatementASTNode()
     : base(ASTNodeType.ASTTYPE_WHILESTATEMENT)
 {
     expr  = null;
     block = null;
 }