#ifndef MAIN_H
#define MAIN_H#ifndef MAIN_H
#define MAIN_HTo get access to ast_program program_ast
#include "parser.hpp"
void error_message(int lineno, const char *error, ...);Declare ast_program program_ast as a global variable
so parser.y can set it and we can use it in main.cpp
extern ast_program program_ast;
#endif