Compiler/lexer.cpp at main · ItmoSE/Compiler · GitHub

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#include "lexer.hpp"
#include <stdexcept>

Lexer::Lexer(std::string str) : src_(std::move(str)) {}

bool Lexer::isAtEnd() const { return pos_ >= src_.size(); }
char Lexer::peek() const { return isAtEnd() ? '\0' : src_[pos_]; }

char Lexer::advance() {
  if (isAtEnd())
    return '\0';
  char c = src_[pos_++];
  if (c == '\n') {
    line_++;
    col_ = 1;
  } else {
    col_++;
  }
  return c;
}

std::vector<Token> Lexer::tokenize() {
  std::vector<Token> out;

  while (!isAtEnd()) {
    char c = peek();

    if (c == ' ' || c == '\t' || c == '\r' || c == '\n') {
      advance();
      continue;
    }

    std::size_t startPos = pos_;
    int startLine = line_;
    int startCol = col_;

    // string literal
    if (c == '"') {
      advance(); // opening quote

      std::string value;
      while (!isAtEnd() && peek() != '"') {
        char ch = advance();
        if (ch == '\\') {
          if (isAtEnd())
            throw std::runtime_error("unterminated escape at " +
                                     std::to_string(startLine) + ":" +
                                     std::to_string(startCol));
          char esc = advance();
          switch (esc) {
          case 'n':
            value.push_back('\n');
            break;
          case 't':
            value.push_back('\t');
            break;
          case '"':
            value.push_back('"');
            break;
          case '\\':
            value.push_back('\\');
            break;
          default:
            value.push_back(esc);
            break;
          }
        } else {
          value.push_back(ch);
        }
      }

      if (isAtEnd())
        throw std::runtime_error("unterminated string at " +
                                 std::to_string(startLine) + ":" +
                                 std::to_string(startCol));

      advance(); // closing quote

      out.push_back(Token{TokenKind::String, value, startLine, startCol});
      continue;
    }

    // Identifier / Keyword
    if (isIdentStart(c)) {
      advance();
      while (!isAtEnd() && isIdentCont((unsigned char)peek()))
        advance();

      Token t;
      t.lexeme = src_.substr(startPos, pos_ - startPos);
      t.line = startLine;
      t.col = startCol;

      t.kind = (t.lexeme == "var" || t.lexeme == "while" || t.lexeme == "if" ||
                t.lexeme == "else" || t.lexeme == "print" ||
                t.lexeme == "true" || t.lexeme == "false")
                   ? TokenKind::Keyword
                   : TokenKind::Identifier;

      out.push_back(std::move(t));
      continue;
    }

    // Number
    if (std::isdigit((unsigned char)c)) {
      advance();
      while (!isAtEnd() && std::isdigit((unsigned char)peek()))
        advance();

      Token t;
      t.kind = TokenKind::Number;
      t.lexeme = src_.substr(startPos, pos_ - startPos);
      t.line = startLine;
      t.col = startCol;
      out.push_back(std::move(t));
      continue;
    }

    // Symbol
    char a = advance();
    std::string s{a};
    if (!isAtEnd()) {
      char b = peek();
      if ((a == '=' && b == '=') || (a == '!' && b == '=') ||
          (a == '<' && b == '=') || (a == '>' && b == '=')) {
        s.push_back(advance());
      }
    }

    Token t;
    t.kind = TokenKind::Symbol;
    t.lexeme = std::move(s);
    t.line = startLine;
    t.col = startCol;
    out.push_back(std::move(t));
  }

  out.push_back(Token{TokenKind::End, "", line_, col_});
  return out;
}