Lexer.cpp

#include <stdexcept>
#include <string>
#include <cctype>
#include "Token.h"
#include "Lexer.h"

Lexer::Lexer(std::string text){
 	this->text = text;
 	this->pos = 0;
 	this->current_char = this->text.at(this->pos);
}

void Lexer::error(){
	throw std::invalid_argument("Error parsing input");
}
 	
void Lexer::advance(){
	this->pos++;
	if(this->pos > this->text.length()-1)
		this->current_char = '\0';
	else
		this->current_char = this->text.at(this->pos);
}

void Lexer::skip_whitespace(){
	while(this->current_char!='\0' && this->current_char==' ')
		this->advance();
}

int Lexer::get_integer(){
	std::string result = "";
	while(this->current_char!='\0' && isdigit(this->current_char)){
		result += this->current_char;
		this->advance();
	}

	return stoi(result);
}

Token Lexer::get_next_token() {
	while(this->current_char != '\0'){
		if( isspace(this->current_char) ){
			this->skip_whitespace();
			continue;
		}

		if( isdigit(this->current_char) )
			return Token(INTEGER, this->get_integer());

		if( this->current_char == '+' ){
			this->advance();
			return Token(PLUS, (int)'+');
		}

		if( this->current_char == '-' ){
			this->advance();
			return Token(MINUS, (int)'-');
		}

		if( this->current_char == '*' ){
			this->advance();
			return Token(MUL, (int)'*');
		}

		if (this->current_char == '/' ){
			this->advance();
			return Token(DIV, (int)'/');
		}

		if(this->current_char == '('){
			this->advance();
			return Token(LPAREN, (int)'(');
		}

		if(this->current_char == ')'){
			this->advance();
			return Token(RPAREN, (int)')');
		}

		this->error();
	}
	return Token(EOFE, (int)'\0');
}