C++23, rusty error handling, renamed output repr of tokens

compile_commands.json

@@ -3,7 +3,7 @@
     "arguments": [
       "/usr/bin/clang++",
       "-c",
-      "-std=c++17",
+      "-std=c++23",
       "-Wall",
       "-Wextra",
       "-pedantic",
@@ -15,56 +15,5 @@
     "directory": "/Users/Shautvast/dev/clox",
     "file": "/Users/Shautvast/dev/clox/src/lox.cpp",
     "output": "/Users/Shautvast/dev/clox/target/lox.cpp.o"
-  },
-  {
-    "arguments": [
-      "/usr/bin/clang++",
-      "-c",
-      "-std=c++17",
-      "-Wall",
-      "-Wextra",
-      "-pedantic",
-      "-Werror",
-      "-o",
-      "target/parser.cpp.o",
-      "src/parser.cpp"
-    ],
-    "directory": "/Users/Shautvast/dev/clox",
-    "file": "/Users/Shautvast/dev/clox/src/parser.cpp",
-    "output": "/Users/Shautvast/dev/clox/target/parser.cpp.o"
-  },
-  {
-    "arguments": [
-      "/usr/bin/clang++",
-      "-c",
-      "-std=c++17",
-      "-Wall",
-      "-Wextra",
-      "-pedantic",
-      "-Werror",
-      "-o",
-      "target/scanner.cpp.o",
-      "src/scanner.cpp"
-    ],
-    "directory": "/Users/Shautvast/dev/clox",
-    "file": "/Users/Shautvast/dev/clox/src/scanner.cpp",
-    "output": "/Users/Shautvast/dev/clox/target/scanner.cpp.o"
-  },
-  {
-    "arguments": [
-      "/usr/bin/clang++",
-      "-c",
-      "-std=c++17",
-      "-Wall",
-      "-Wextra",
-      "-pedantic",
-      "-Werror",
-      "-o",
-      "target/tokens.cpp.o",
-      "src/tokens.cpp"
-    ],
-    "directory": "/Users/Shautvast/dev/clox",
-    "file": "/Users/Shautvast/dev/clox/src/tokens.cpp",
-    "output": "/Users/Shautvast/dev/clox/target/tokens.cpp.o"
   }
 ]

makefile

@@ -1,6 +1,6 @@
 TARGET := ./target
 SRC := ./src
-CC := clang++ -c -std=c++17 -Wall -Wextra -pedantic -Werror
+CC := clang++ -c -std=c++23 -Wall -Wextra -pedantic -Werror
 
 SRCS := $(shell find $(SRC) -name '*.c')
 OBJS := $(SRCS:%=$(TARGET)/%.o)

src/error.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <string>
+#include <variant>
+
+using namespace std;
+
+class Error {
+
+public:
+  string message;
+  Error(string _message) : message(_message){};
+};
+
+class Void {};
+
+template <typename R> using Result = std::variant<R, Error>;
+
+template <typename R> bool is_err(Result<R> r) {
+  return std::holds_alternative<Error>(r);
+}
+template <typename R> bool is_ok(Result<R> r) {
+  return std::holds_alternative<R>(r);
+}
+
+template <typename R> R Ok(Result<R> r) { return std::get<R>(r); }
+/// enables rewrapping errors in a new Result type
+template <typename R> Error Err(Result<R> r) { return std::get<Error>(r); }
+template <typename R> string err_msg(Result<R> r) {
+  return std::get<Error>(r).message;
+}

src/lox.cpp

@@ -12,7 +12,7 @@ using namespace std;
 void print_tokens(vector<Token> *list);
 int run_file(string file);
 void run_prompt(void);
-ScanResult run(string source);
+Result<vector<Token>> run(string source);
 
 int main(int argc, char *argv[]) {
   if (argc > 2) {
@@ -36,7 +36,7 @@ int run_file(string filename) {
     exit(1);
   }
 
-  ScanResult scan_result = run(content);
+  Result<vector<Token>> scan_result = run(content);
 
   return EXIT_SUCCESS;
 }
@@ -49,17 +49,22 @@ void run_prompt(void) {
 
     getline(cin, line);
 
-    ScanResult scan_result = run(line.substr(0, line.length()));
+    auto scan_result = run(line.substr(0, line.length()));
     // print_tokens(&scan_result.token_list);
-    if (!scan_result.had_error) {
-      Expression *e = (new Parser())->parse(scan_result.token_list);
-      cout << e->as_string();
-      cout << "\n";
+    if (is_ok(scan_result)) {
+      auto expression = (new Parser())->parse(get<vector<Token>>(scan_result));
+      if (is_ok(expression)) {
+        cout << Ok(expression)->as_string() << "\n";
+      } else {
+        cout << err_msg(expression) << "\n";
+      }
+    } else {
+      cout << err_msg(scan_result) << "\n";
     }
   }
 }
 
-ScanResult run(string source) {
+Result<vector<Token>> run(string source) {
   Scanner *scanner = new Scanner(source);
   return scanner->scan_tokens();
 }

src/parser.cpp

@@ -1,4 +1,5 @@
 #include "parser.hpp"
+
 #include <iostream>
 #include <memory>
 
@@ -61,7 +62,7 @@ string Literal::as_string() {
 }
 
 // class Parser
-Expression *Parser::parse(vector<Token> tokenlist) {
+Result<Expression *> Parser::parse(vector<Token> tokenlist) {
   tokens = tokenlist;
   current_token = 0;
   return expression();
@@ -101,25 +102,25 @@ bool Parser::match(int count, ...) {
   return false;
 };
 
-Token *Parser::consume(Token::Type typ, string message) {
+Result<Token *> Parser::consume(Token::Type typ, string message) {
   if (check(typ)) {
     return advance();
   }
-  throw error(peek(), message);
+  return error(peek(), message);
 }
 
-runtime_error Parser::error(Token token, string message) {
+Error Parser::error(Token token, string message) {
   std::cout << token.as_string() << " " << message;
-  return runtime_error(message); // TODO no exceptions
+  return Error(message); // TODO no exceptions
 }
 
-Expression *Parser::primary() {
+Result<Expression *> Parser::primary() {
   if (match(1, Token::Type::FALSE))
     return new Literal(false);
   if (match(1, Token::Type::TRUE))
     return new Literal(true);
   if (match(1, Token::Type::NIL))
-    return new Literal(new Void());
+    return new Literal(new NilType());
   if (match(1, Token::Type::NUMBER)) {
     return new Literal(stod(previous()->literal));
   }
@@ -127,62 +128,90 @@ Expression *Parser::primary() {
     return new Literal(previous()->literal);
   }
   if (match(1, Token::Type::LEFT_PAREN)) {
-    Expression *expr = expression();
-    consume(Token::Type::RIGHT_PAREN, "Expect ')'.");
-    return new Grouping(expr);
+    auto expr = expression();
+    Result<Token *> r = consume(Token::Type::RIGHT_PAREN, "Expect ')'.");
+    if (is_err(r)) {
+      return Err(r);
+    }
+    return new Grouping(Ok(expr));
   }
-  throw runtime_error("Expected an expression");
+  return Error("Expected an expression");
 }
 
-Expression *Parser::unary() {
+Result<Expression *> Parser::unary() {
   if (match(2, Token::BANG, Token::Type::MINUS)) {
     Token *op = previous();
-    Expression *right = unary();
-    return new Unary(op, right);
+    Result<Expression *> right = unary();
+    if (is_ok(right)) {
+      return new Unary(op, Ok(right));
+    }
   }
   return primary();
 }
 
-Expression *Parser::expression() { return equality(); }
+Result<Expression *> Parser::expression() { return equality(); }
 
-Expression *Parser::factor() {
-  Expression *expr = unary();
+Result<Expression *> Parser::factor() {
+  Result<Expression *> expr = unary();
+  if (is_err(expr)) {
+    return expr;
+  }
   while (match(2, Token::Type::SLASH, Token::Type::STAR)) {
     Token *op = previous();
-    Expression *right = unary();
-    expr = new Binary(expr, op, right);
+    auto right = unary();
+    if (is_err(right)) {
+      return right;
+    }
+    expr = new Binary(Ok(expr), op, Ok(right));
   }
   return expr;
 }
 
-Expression *Parser::term() {
-  Expression *expr = factor();
+Result<Expression *> Parser::term() {
+  auto expr = factor();
+  if (is_err(expr)) {
+    return expr;
+  }
   while (match(2, Token::Type::MINUS, Token::Type::PLUS)) {
     Token *op = previous();
-    Expression *right = factor();
-    expr = new Binary(expr, op, right);
+    auto right = factor();
+    if (is_err(right)) {
+      return right;
+    }
+    expr = new Binary(Ok(expr), op, Ok(right));
   }
   return expr;
 }
 
-Expression *Parser::equality(void) {
-  Expression *expr = comparison();
-
+Result<Expression *> Parser::equality(void) {
+  auto expr = comparison();
+  if (is_err(expr)) {
+    return expr;
+  }
   while (match(2, Token::Type::BANG_EQUAL, Token::Type::BANG_EQUAL)) {
     Token *op = previous();
-    Expression *right = comparison();
-    return new Binary(expr, op, right);
+    auto right = comparison();
+    if (is_err(right)) {
+      return right;
+    }
+    return new Binary(Ok(expr), op, Ok(right));
   }
   return expr;
 }
 
-Expression *Parser::comparison(void) {
-  Expression *expr = term();
+Result<Expression *> Parser::comparison(void) {
+  auto expr = term();
+  if (is_err(expr)) {
+    return expr;
+  }
   while (match(4, Token::Type::GREATER, Token::Type::GREATER_EQUAL,
                Token::Type::LESS, Token::Type::LESS_EQUAL)) {
     Token *op = previous();
-    Expression *right = term();
-    expr = new Binary(expr, op, right);
+    auto right = term();
+    if (is_err(right)) {
+      return right;
+    }
+    expr = new Binary(Ok(expr), op, Ok(right));
   }
   return expr;
 }

src/parser.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include "error.hpp"
 #include "tokens.hpp"
 #include <memory>
 #include <vector>
@@ -53,7 +54,7 @@ public:
 };
 
 /// empty class that is the type of the Nil value
-class Void {};
+class NilType {};
 
 /// encapsulates a value: numeric, string etc
 class Literal : public Expression {
@@ -66,16 +67,16 @@ public:
     double_t numeric;
     bool boolean;
     string str;
-    Void dummy;
+    NilType dummy;
 
     Value(double_t _numeric) : numeric(_numeric) {}
     Value(bool _boolean) : boolean(_boolean) {}
     Value(string _str) : str(_str) {}
-    Value(Void v) : dummy(v) {}
+    Value(NilType v) : dummy(v) {}
     ~Value() {}
   } value;
 
-  Literal(Void v) : valuetype(ValueType::Nil), value(v){};
+  Literal(NilType v) : valuetype(ValueType::Nil), value(v){};
   Literal(double_t _numeric) : valuetype(ValueType::Numeric), value(_numeric){};
   Literal(string _str) : valuetype(ValueType::String), value(_str){};
   Literal(bool _boolean) : valuetype(ValueType::Boolean), value(_boolean){};
@@ -106,26 +107,26 @@ class Parser {
   /// checks if the current token is of the specified type and
   /// moves the token forward if so, otherwise throws an exception with
   /// the specified message
-  Token *consume(Token::Type typ, string message);
+  Result<Token *> consume(Token::Type typ, string message);
   /// throws an exception for the specified token with the specified message
-  runtime_error error(Token token, string message);
+  Error error(Token token, string message);
   /// tries to parse the token as a primary value (string, number etc)
-  Expression *primary();
+  Result<Expression *> primary();
   /// tries to parse the tokens as a unary expression
-  Expression *unary();
+  Result<Expression *> unary();
   /// tries to parse the tokens
-  Expression *expression();
+  Result<Expression *> expression();
   /// tries to parse the tokens as a multiplication or division
-  Expression *factor();
+  Result<Expression *> factor();
   /// tries to parse the tokens as an addition or subtraction
-  Expression *term();
+  Result<Expression *> term();
   /// tries to parse the tokens as an equality (`a == b` / `a!= b`)
-  Expression *equality(void);
+  Result<Expression *> equality();
   /// tries to parse the tokens as a comparison (`a > b` / `a >= b` / `a < b` /
   /// `a <= b` )
-  Expression *comparison(void);
+  Result<Expression *> comparison();
 
 public:
   /// public method for parsing expressions
-  Expression *parse(vector<Token> tokenlist);
+  Result<Expression *> parse(vector<Token> tokenlist);
 };

src/scanner.cpp

@@ -1,4 +1,5 @@
 #include "scanner.hpp"
+#include "error.hpp"
 #include "tokens.hpp"
 #include <cstdbool>
 #include <iostream>
@@ -23,17 +24,15 @@ Scanner::Scanner(string _source)
     : had_error(false), current_pos(0), start(0), current_line(1),
       source(_source), token_list(vector<Token>()) {}
 
-ScanResult Scanner::scan_tokens() {
+Result<vector<Token>> Scanner::scan_tokens() {
   while (current_pos < source.length()) {
     start = current_pos;
-    scan_token();
+    Result<Void> r = scan_token();
+    if (is_err(r)) {
+      return Err(r);
+    }
   }
-
-  ScanResult scan_result;
-  scan_result.token_list = token_list;
-  scan_result.had_error = had_error;
-
-  return scan_result;
+  return token_list;
 }
 
 void Scanner::add_token(Token::Type type) {
@@ -51,7 +50,7 @@ char Scanner::advance() {
   return c;
 }
 
-void Scanner::scan_token() {
+Result<Void> Scanner::scan_token() {
   char c = advance();
 
   switch (c) {
@@ -119,10 +118,11 @@ void Scanner::scan_token() {
     } else if (is_alpha(c)) {
       identifier();
     } else {
-      error("Unexpected character.");
+      return Error{"Unexpected character."};
     }
     break;
   }
+  return Void{};
 }
 
 void Scanner::identifier() {
@@ -159,7 +159,7 @@ void Scanner::scan_string() {
   }
 
   if (is_at_end()) {
-    error("Unterminated string.");
+    report("Unterminated string.");
     return;
   }
 
@@ -202,7 +202,7 @@ bool Scanner::is_alphanumeric(char c) { return is_alpha(c) || is_digit(c); }
 
 bool Scanner::is_at_end(void) { return current_pos >= source.length(); }
 
-void Scanner::error(string message) { report("", message); }
+void Scanner::report(string message) { report("", message); }
 
 void Scanner::report(string where, std::string message) {
   cout << "*[Line " << current_line << "] Error " << where << " : " << message

src/scanner.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include "error.hpp"
 #include "tokens.hpp"
 #include <cstdbool>
 #include <string>
@@ -23,11 +24,11 @@ private:
 
 public:
   Scanner(string s);
-  ScanResult scan_tokens();
+  Result<vector<Token>> scan_tokens();
+  Result<Void> scan_token();
   void add_token(Token::Type type);
   void add_token(Token::Type type, string literal);
   char advance();
-  void scan_token();
   void identifier();
   void number();
   bool is_digit(char c);
@@ -38,6 +39,6 @@ public:
   bool is_alpha(char c);
   bool is_alphanumeric(char c);
   bool is_at_end(void);
-  void error(string message);
+  void report(string message);
   void report(string where, string message);
 };

src/tokens.cpp

@@ -7,14 +7,12 @@ Token::Token(Token::Type _tokentype, string _lexeme, string _literal, int _line)
 
 string token_name(Token::Type tokentype) {
   static const std::string tokens[] = {
-      "END_OF_FILE", "LEFT_PAREN", "RIGHT_PAREN",   "LEFT_BRACE", "RIGHT_BRACE",
-      "COMMA",       "DOT",        "MINUS",         "PLUS",       "SEMICOLON",
-      "SLASH",       "STAR",       "BANG",          "BANG_EQUAL", "EQUAL",
-      "EQUAL_EQUAL", "GREATER",    "GREATER_EQUAL", "LESS",       "LESS_EQUAL",
-      "IDENTIFIER",  "STRING",     "NUMBER",        "AND",        "CLASS",
-      "ELSE",        "FALSE",      "FUN",           "FOR",        "IF",
-      "NIL",         "OR",         "PRINT",         "RETURN",     "SUPER",
-      "THIS",        "TRUE",       "VAR",           "WHILE"};
+      "EOF",    "(",      ")",   "{",     "}",     ",",      "*",
+      "-",      "+",      ";",   "/",     "*",     "!",      "!=",
+      "=",      "==",     ">",   ">=",    "<",     "<=",     "IDENTIFIER",
+      "string", "number", "and", "class", "else",  "false",  "fun",
+      "for",    "if",     "Nil", "or",    "print", "return", "super",
+      "this",   "true",   "var", "while"};
   return tokens[(int)tokentype];
 }