first commit

README.md

@@ -0,0 +1 @@
+## C++ Version of https://ruslanspivak.com/lsbasi-part1/

chapter01/interpreter.cpp

@@ -0,0 +1,106 @@
+#include <string>
+#include <cctype>
+#include <stdexcept>
+#include <iostream>
+
+namespace lsbasi {
+
+	enum TokenType {
+  		_INTEGER,
+  		_PLUS,
+  		_EOF
+	};
+
+	class Token{
+		public:
+			TokenType type;
+			char value;
+			Token(TokenType type, char value): type(type), value(value){}
+	};
+
+	class Interpreter {
+
+		private:
+
+			std::string text;
+			int pos;
+			Token * current_token;
+
+			int error(){
+				throw std::runtime_error("Error parsing input");
+			}
+
+			Token * get_next_token(){
+
+				if (pos > text.size() - 1)
+					return new Token(_EOF, 0);
+
+				char current_char = text[pos];
+
+				if (std::isdigit(current_char)){
+					pos++;
+					return new Token (_INTEGER, current_char);
+				}
+
+				if (current_char == '+'){
+					pos++;
+					return new Token (_PLUS, current_char);
+				}
+
+				error();
+
+			}
+
+			void eat (TokenType type){
+				if (current_token->type == type)
+					current_token = get_next_token();
+				else
+					error();
+			}
+
+
+		public:
+
+			Interpreter(std::string text): text(text), pos(0), current_token(NULL){}
+
+			int expr(){
+
+				current_token = get_next_token();
+				Token * left = current_token;
+				eat(_INTEGER);
+
+				Token * op = current_token;
+				eat(_PLUS);
+
+				Token * right = current_token;
+				eat(_INTEGER);
+
+				int result = (left->value - '0') + (right->value - '0');
+
+				delete right;
+				delete op;
+				delete left;
+
+				return result;
+			}
+
+	};
+
+};
+
+int main (){
+
+	while(true){
+
+		std::string text;
+		std::cout << "calc> "; 
+		std::cin >> text;
+		lsbasi::Interpreter interpreter(text);
+		std::cout << interpreter.expr() << std::endl;
+
+		//ctrl+c to exit
+
+	}
+
+	return 0;
+}

chapter02/interpreter.cpp

@@ -0,0 +1,140 @@
+#include <string>
+#include <cctype>
+#include <stdexcept>
+#include <iostream>
+
+namespace lsbasi {
+
+	enum TokenType {
+  		_INTEGER,
+  		_PLUS,
+		_MINUS,
+  		_EOF
+	};
+
+	class Token{
+		public:
+			TokenType type;
+			std::string value;
+			Token(TokenType type, std::string value): type(type), value(value){}
+	};
+
+	class Interpreter {
+
+		private:
+
+			std::string text;
+			int pos;
+			Token * current_token;
+			char current_char;
+
+			int error () {
+				throw std::runtime_error("Error parsing input");
+			}
+
+			void advance () {
+				pos++;
+				if (pos > text.size() - 1)
+					current_char = 0;
+				else
+					current_char = text[pos];
+			}
+
+			void skip_whitespace () {
+				while((current_char != 0) && (current_char == ' ')) 
+					advance();
+			}
+
+			std::string integer () {
+				std::string result;
+				while((current_char != 0) && std::isdigit(current_char)){
+					result += current_char; 
+					advance();
+				}
+				return result;
+			}
+
+			Token * get_next_token () {
+
+				while(current_char != 0){
+					skip_whitespace();
+					if (std::isdigit(current_char))
+						return new Token(_INTEGER, integer());
+
+					if (current_char == '+'){
+						advance();
+						return new Token (_PLUS, "+");
+					}
+
+					if (current_char == '-'){
+						advance();
+						return new Token (_MINUS, "-");
+					}
+
+					error();
+
+				}
+
+			}
+
+			void eat (TokenType type){
+				if (current_token->type == type)
+					current_token = get_next_token();
+				else
+					error();
+			}
+
+
+		public:
+
+			Interpreter(std::string text): text(text), pos(0), current_token(NULL), current_char(text[pos]) {}
+
+			int expr(){
+
+				int result;
+
+				current_token = get_next_token();
+				Token * left = current_token;
+				eat(_INTEGER);
+
+				Token * op = current_token;
+				if (op->type == _PLUS)
+					eat(_PLUS);
+				else
+					eat(_MINUS);
+
+				Token * right = current_token;
+				eat(_INTEGER);
+
+				if(op->type == _PLUS) 
+					result = std::stoi(left->value) + std::stoi(right->value);
+				else
+					result = std::stoi(left->value) - std::stoi(right->value);
+
+				delete right;
+				delete op;
+				delete left;
+
+				return result;
+			}
+
+	};
+
+};
+
+int main (){
+
+	while(true){
+
+		std::string text;
+		std::cout << "calc> "; 
+		std::cin >> text;
+		lsbasi::Interpreter interpreter(text);
+		std::cout << interpreter.expr() << std::endl;
+
+		//ctrl+c to exit
+
+	}
+
+	return 0;
+}

chapter03/interpreter.cpp

@@ -0,0 +1,142 @@
+#include <string>
+#include <cctype>
+#include <stdexcept>
+#include <iostream>
+
+namespace lsbasi {
+
+	enum TokenType {
+  		_INTEGER,
+  		_PLUS,
+		_MINUS,
+  		_EOF
+	};
+
+	class Token{
+		public:
+			TokenType type;
+			std::string value;
+			Token(TokenType type, std::string value): type(type), value(value){}
+	};
+
+	class Interpreter {
+
+		private:
+
+			std::string text;
+			int pos;
+			Token * current_token;
+			char current_char;
+
+			int error () {
+				throw std::runtime_error("Error parsing input");
+			}
+
+			void advance () {
+				pos++;
+				if (pos > text.size() - 1)
+					current_char = 0;
+				else
+					current_char = text[pos];
+			}
+
+			void skip_whitespace () {
+				while((current_char != 0) && (current_char == ' ')) 
+					advance();
+			}
+
+			std::string integer () {
+				std::string result;
+				while((current_char != 0) && std::isdigit(current_char)){
+					result += current_char; 
+					advance();
+				}
+				return result;
+			}
+
+			Token * get_next_token () {
+
+				while(current_char != 0){
+					skip_whitespace();
+					if (std::isdigit(current_char))
+						return new Token (_INTEGER, integer());
+
+					if (current_char == '+'){
+						advance();
+						return new Token (_PLUS, "+");
+					}
+
+					if (current_char == '-'){
+						advance();
+						return new Token (_MINUS, "-");
+					}
+
+					error();
+
+				}
+
+				return new Token(_EOF, "");
+
+			}
+
+			void eat (TokenType type){
+				if (current_token->type == type){
+					delete current_token;
+					current_token = get_next_token();
+				}else
+					error();
+			}
+
+			int term(){
+				std::string res = current_token->value;
+				eat(_INTEGER);
+				return std::stoi(res);
+			}
+
+
+		public:
+
+			Interpreter(std::string text): text(text), pos(0), current_token(NULL), current_char(text[pos]) {}
+
+			int expr(){
+
+				current_token = get_next_token();
+
+				int result = term();
+
+				while((current_token->type == _PLUS) || (current_token->type == _MINUS)){
+
+					Token * tk = current_token;
+					if (tk->type == _PLUS){
+						eat(_PLUS);
+						result += term(); 
+					}
+					if (tk->type == _MINUS){
+						eat(_MINUS);
+						result -= term(); 
+					}
+				}
+
+				return result;
+			}
+
+	};
+
+};
+
+int main (){
+
+	while(true){
+
+		std::string text;
+		std::cout << "calc> "; 
+		std::cin >> text;
+		lsbasi::Interpreter interpreter(text);
+		std::cout << interpreter.expr() << std::endl;
+
+		//ctrl+c to exit
+
+	}
+
+	return 0;
+}