private void EnterScope(AstNode node)
 {
     _stack.Push(_symbols);
     _symbols = new SymbolTable(_symbols);
     node.Annotate(new SymbolTableAnnotation(_symbols));
 }
 private void ExitScope()
 {
     _symbols = _stack.Pop();
 }
 public SymbolTable(SymbolTable parent = null)
 {
     _parent = parent;
 }