public IfStmt(Expr Condition, Stmt ThenBranch, Stmt ElseBranch)
 {
     this.Condition  = Condition;
     this.ThenBranch = ThenBranch;
     this.ElseBranch = ElseBranch;
 }
 public WhileStmt(Expr Condition, Stmt Body)
 {
     this.Condition = Condition;
     this.Body      = Body;
 }
 private void Execute(Stmt stmt)
 {
     stmt.Accept(this);
 }