a

a.cpp

/*                    *
 *  Bython ver.0.0.0  *
 *   made by:         *
 *          akouryy   *
 *        hirorisuu   *
 *         satouuta   *
 *                    */
#include <stdlib.h>

#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;

typedef struct{
	int index;
	int error;
} parse;

int expr1(string const, parse*);
int expr2(string const, parse*);
int expr3(string const, parse*);
/*
	{0 to 9}                                ... number
	S {a to z | A to Z | _} S               ... name
	[expr1 {, expr1}]                       ... funarg
	name \( funarg \)                       ... function
	expr2 {(+ | -) expr2}                   ... expr1
	expr3 {(* | /) expr3}                   ... expr2
	S (\( expr1 \) | number | function) S   ... expr3
*/

string bython(string program){
	parse option = {0, 0};
	int ret = expr1(program, &option);
	ostringstream stream;
	stream << ret << "(" << (option.error?"Error, ":"") << "index: " << option.index << ")";
	return stream.str();
}
void skips(string const program, parse* option){
	while(program[option->index] == ' '){
		option->index++;
	}
}

int number(string program, parse* option){
	int result = 0;
	if(program[option->index] < '0' || '9' < program[option->index]){
		option->error = 1;
		return 0;
	}
	while('0' <= program[option->index] && program[option->index] <= '9'){
		result = result * 10 + program[option->index] - '0';
		option->index++;
	}
	return result;
}

string name(string program, parse* option){
	if(!(  'a' <= program[option->index] && program[option->index] <= 'z'
		|| 'A' <= program[option->index] && program[option->index] <= 'Z'
		|| '_' == program[option->index])){
		option->error = 1;
		return "";
	}
	int old_index = option->index;
	string result;
	while( 'a' <= program[option->index] && program[option->index] <= 'z'
		|| 'A' <= program[option->index] && program[option->index] <= 'Z'
		|| '0' <= program[option->index] && program[option->index] <= '9'
		|| '_' == program[option->index]){
		result += program[option->index];
		option->index++;
	}
	return result;
}

vector<int> funarg(string program, parse* option){
	vector<int> args;
	args.push_back(expr1(program, option));
	if(option->error){
		return args;
	}
	while(1){
		int val = expr1(program, option);
		if(option->error){
			return args;
		}
		args.push_back(val);
	}
}

int function(string program, parse* option){
	int old_index = option->index;
	vector<int> args;
	string fname = name(program, option);
	if(program[option->index] == '('){
		option->index++;
		args = funarg(program, option);
		if(program[option->index] != ')'){
			option->index = old_index;
			option->error = 1;
			return 0;
		}
		option->index++;
	}else{
		option->error = 1;
		return 0;
	}
	if(fname == "exit" && args.empty()){
		exit(0);
	}else if(fname == "exit" && args.size() == 1){
		exit(args[0]);
	}
	return 0; //TODO: 後で変える
}

int expr1(string program, parse* option){
	int result = expr2(program, option);
	while(1){
		switch(program[option->index]){
		case '+':
			option->index++;
			result += expr2(program, option);
			break;
		case '-':
			option->index++;
			result -= expr2(program, option);
			break;
		default:
			return result;
		}
		if(option->error){
			option->index--;
			option->error=0;
			return result;
		}
	}
}
int expr2(string program, parse* option){
	int result = expr3(program, option);
	while(1){
		switch(program[option->index]){
		case '*':
			option->index++;
			result *= expr3(program, option);
			break;
		case '/':
			option->index++;
			result /= expr3(program, option);
			break;
		default:
			return result;
		}
		if(option->error){
			option->index--;
			option->error=0;
			return result;
		}
	}
}
int expr3(string program, parse* option){
	int result = 0;
	int old_index = option->index;
	skips(program, option);
	if(program[option->index] == '('){
		option->index++;
		result = expr1(program, option);
		if(program[option->index] != ')'){
			option->index = old_index;
			option->error = 1;
			return 0;
		}
		option->index++;
	}else{
		result = number(program, option);
		if(option->error){
			option->error = 0;
			function(program, option);
		}
	}
	skips(program, option);
	return result;
}


int main(void){
	while(1){
		cout << "> ";
		string s;
		getline(cin, s);
		if(!s.empty()){
			cout << bython(s) << endl;
		}
	}
}