#ifndef PARSER_H
#define PARSER_H

#include "expression.h"
#include <iterator>
#include <string>
#include <boost/shared_ptr.hpp>

// parser is a singleton that creates a hierarchy of Expression nodes from an input stream
// note that this parser handles bracketed expressions like 3 * ( 1 + 2 )
class Parser
{
	private:
		Parser();
		Parser(const Parser& p);
		~Parser();
		Parser& operator=(const Parser& p);
		
		typedef std::istream_iterator<std::string> Tokenizer;
		
		ExpressionPtr get_add_expression(Tokenizer& tok) const;
		ExpressionPtr get_mult_expression(Tokenizer& tok) const;
		ExpressionPtr get_integer_or_bracket(Tokenizer& tok) const;
		bool is_numeric(const std::string& s) const;
	
	public:
		static Parser* get_parser();
		ExpressionPtr parse(Tokenizer& tok) const;
		class BadInput
		{
			private:
				std::string msg;
				
			public:
				BadInput(const std::string& m = std::string());
				const std::string& get_message() const;
		};
};

#endif