crafting-interpreters/cclox_src/parser/parser.cc

#include "parser.hh"
#include "expr.hh"
#include "stmt.hh"
#include "../error_handler.hh"
#include "../tokenizer.hh"
#include <cassert>

extern ErrorHandler error_handler;

std::vector<Stmt> Parser::parse() {
  std::vector<Stmt> statements{};
  while (!is_at_end()) {
    statements.push_back(declaration());
  }

  return statements;
}

Stmt Parser::declaration() {
  try {
    if (match({TokenType::VAR})) {
      return var_declaration();
    }

    return statement();
  } catch (ParseException e) {
    synchronize();
    return Expression(Literal(Object{}));
  }
}

Stmt Parser::var_declaration() {
  Token name       = consume(TokenType::IDENTIFIER, "Expect variable name.");
  Expr initializer = Literal(Object{});

  if (match({TokenType::EQUAL})) {
    initializer = expression();
  }

  consume(TokenType::SEMICOLON, "Expect ';' after variable declaration");
  return Var(name, initializer);
}

Stmt Parser::statement() {
  if (match({TokenType::PRINT})) {
    return print_statement();
  }

  if (match({TokenType::LEFT_BRACE})) {
    return Block(block_statement());
  }

  return expression_statement();
}

std::vector<Stmt> Parser::block_statement() {
  std::vector<Stmt> statements{};

  while (!check(TokenType::RIGHT_BRACE) && !is_at_end()) {
    statements.push_back(declaration());
  }

  consume(TokenType::RIGHT_BRACE, "Expect '}' after block.");
  return statements;
}

Stmt Parser::print_statement() {
  Expr value{expression()};
  consume(TokenType::SEMICOLON, "Expect ';' after value.");
  return Print(value);
}

Stmt Parser::expression_statement() {
  Expr value{expression()};
  consume(TokenType::SEMICOLON, "Expect ';' after value.");
  return Expression(value);
}

Expr Parser::expression() {
  return assignment();
}

Expr Parser::assignment() {
  Expr expr = equality();

  if (match({TokenType::EQUAL})) {
    Token equals = previous();
    Expr value   = assignment();

    if (expr.type == ExprType::VARIABLE) {
      std::shared_ptr<_Variable> ptr = std::get<std::shared_ptr<_Variable>>(expr.value);
      assert(ptr != nullptr);
      Token name = ptr->name;
      return Assign(name, value);
    }

    error_handler.error(equals, "Invalid assignment target.");
  }

  return expr;
}

Expr Parser::equality() {
  Expr expr = comparison();

  while (match({TokenType::BANG_EQUAL, TokenType::EQUAL_EQUAL})) {
    Token op   = previous();
    Expr right = comparison();
    expr       = Binary(expr, op, right);
  }

  return expr;
}

Expr Parser::comparison() {
  Expr expr = term();

  while (match({TokenType::GREATER, TokenType::GREATER_EQUAL, TokenType::LESS, TokenType::LESS_EQUAL})) {
    Token op   = previous();
    Expr right = term();
    expr       = Binary(expr, op, right);
  }

  return expr;
}

Expr Parser::term() {
  Expr expr = factor();

  while (match({TokenType::MINUS, TokenType::PLUS})) {
    Token op = previous();
    Expr right = factor();
    expr = Binary(expr, op, right);
  }

  return expr;
}

Expr Parser::factor() {
  Expr expr = unary();

  while (match({TokenType::SLASH, TokenType::STAR})) {
    Token op   = previous();
    Expr right = unary();
    expr       = Binary(expr, op, right);
  }

  return expr;
}

Expr Parser::unary() {
  if (match({TokenType::BANG, TokenType::MINUS})) {
    Token op   = previous();
    Expr right = unary();

    return Unary(op, right);
  }

  return primary();
}

Expr Parser::primary() {
  if (match({TokenType::FALSE})) {
    return Literal(false);
  }

  if (match({TokenType::TRUE})) {
    return Literal(true);
  }

  if (match({TokenType::NIL})) {
    return Literal(Object{});
  }

  if (match({TokenType::NUMBER, TokenType::STRING})) {
    return Literal(previous().literal);
  }

  if (match({TokenType::IDENTIFIER})) {
    return Variable(previous());
  }

  if (match({TokenType::LEFT_PAREN})) {
    Expr expr = expression();
    consume(TokenType::RIGHT_PAREN, "Expect ')' after expression.");
    return Grouping(expr);
  }

  throw error(peek(), "Expect expression.");
}

Token Parser::advance() {
  if (!is_at_end()) {
    ++current;
  }

  return previous();
}

Token Parser::peek() {
  return tokens.at(current);
}

Token Parser::previous() {
  return tokens.at(current - 1);
}

Token Parser::consume(TokenType type, std::string &&message) {
  if (check(type)) {
    return advance();
  }

  throw error(peek(), message);
}

bool Parser::match(std::vector<TokenType> types) {
  for (const auto &type : types) {
    if (check(type)) {
      advance();
      return true;
    }
  }

  return false;
}

bool Parser::check(TokenType type) {
  if (is_at_end()) {
    return false;
  }

  return peek().type == type;
}

bool Parser::is_at_end() {
  return peek().type == TokenType::EOFILE;
}

ParseException Parser::error(Token token, std::string &message) {
  error_handler.error(token, message);
  return ParseException{};
}

ParseException Parser::error(Token token, std::string &&message) {
  return error(token, message);
}

void Parser::synchronize() {
  advance();

  while (!is_at_end()) {
    if (previous().type == TokenType::SEMICOLON) {
      return;
    }

    switch (peek().type) {
      case TokenType::CLASS:
      case TokenType::FUN:
      case TokenType::VAR:
      case TokenType::FOR:
      case TokenType::IF:
      case TokenType::WHILE:
      case TokenType::PRINT:
      case TokenType::RETURN:
        return;
      default:
        break;
    }

    advance();
  }
}