parse.hpp

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#ifndef PARSE_HPP_
#define PARSE_HPP_

#include <istream>
#include <locale>
#include <ostream>
#include <stdexcept>
#include <string>
#include <vector>

#include "variables.hpp"

class parse_error : public std::runtime_error {
public:
  parse_error(std::string const& msg) : runtime_error{msg} {}
};

class parser
{
public:
  enum kind : int { eof, identifier, number,
    plus='+', minus='-', times='*', slash='/', lparen = '(', rparen=')', equal='=' };

  parser(std::istream& input);

  bool get_expr(double& result);

private:
  std::string charify(char c);
  bool get_number(std::string const& token, double& result);
  bool get_add_expr(double& result);
  bool get_mul_expr(double& result);
  bool get_primary(double& result);
  bool get_unary(double& result);
  kind get_token(std::string& token);
  void get_identifier(std::string& identifier);

  void push_back(std::string const& token, kind k) { token_ = token; kind_ = k; }

  bool isalpha(char c) const { return ctype_.is(ctype_.alpha, c); }
  bool isalnum(char c) const { return ctype_.is(ctype_.alnum, c); }
  bool isdigit(char c) const { return ctype_.is(ctype_.digit, c); }
  bool isprint(char c) const { return ctype_.is(ctype_.print, c); }

  std::istream& input_;             
  std::ctype<char> const& ctype_;   
  std::string token_;               
  kind kind_;                       
};

void parse_loop(std::istream& input, std::ostream& output);

#endif