diff --git a/.clangd b/.clangd
new file mode 100644
index 0000000..d567e73
--- /dev/null
+++ b/.clangd
@@ -0,0 +1,5 @@
+CompileFlags:
+  Remove:
+  - '-fmodules-ts'
+  - '-fmodule-mapper=CMakeFiles/stela.dir/main.cpp.o.modmap'
+  - '-fdeps-format=p1689r5'
diff --git a/parser.cpp b/parser.cpp
new file mode 100644
index 0000000..6930f7c
--- /dev/null
+++ b/parser.cpp
@@ -0,0 +1,154 @@
+#include "parser.hpp"
+#include <cstdlib>
+
+using namespace stela;
+
+static inline auto in_range(char ch, char begin, char end) -> bool
+{
+    return ch >= begin && ch <= end;
+}
+
+static inline auto whitespace_char(char ch) -> bool
+{
+    return ch == ' ' or ch == '\t' or ch == '\n';
+}
+
+static inline auto id_start_char(char ch) -> bool
+{
+    return in_range(ch, 'a', 'z') or in_range(ch, 'A', 'Z') or ch == '_';
+}
+
+static inline auto id_char(char ch) -> bool
+{
+    return in_range(ch, 'a', 'z') or in_range(ch, 'A', 'Z')
+        or in_range(ch, '0', '1') or ch == '_';
+}
+
+auto Lexer::next() -> Token
+{
+    auto pos = this->pos();
+    if (done()) {
+        return token(TokenType::Eof, pos);
+    }
+    char ch = current();
+    if (whitespace_char(ch)) {
+        step();
+        return next();
+    }
+    if (id_start_char(ch)) {
+        std::string value;
+        value.push_back(ch);
+        step();
+        while (not done() and id_char(current())) {
+            value.push_back(current());
+            step();
+        }
+        if (this->keyword_map.contains(value)) {
+            return token(this->keyword_map[value], pos);
+        }
+        size_t id = this->symbol_values.size();
+        this->symbol_values.push_back(value);
+        return Token { TokenType::Id, pos, id };
+    }
+    if (in_range(ch, '1', '9')) {
+        std::string value;
+        value.push_back(ch);
+        step();
+        while (not done() and in_range(ch, '0', '9')) {
+            value.push_back(current());
+            step();
+        }
+        int64_t int_value = std::strtoll(value.c_str(), nullptr, 10);
+        size_t id = this->symbol_values.size();
+        this->int_values.push_back(int_value);
+        return Token { TokenType::Id, pos, id };
+    }
+    if (ch == '0') {
+        step();
+        int64_t int_value = 0;
+        size_t id = this->symbol_values.size();
+        this->int_values.push_back(int_value);
+        return Token { TokenType::Id, pos, id };
+    }
+    if (ch == '"') {
+        // TODO string
+    }
+    if (ch == '#') {
+        while (not done() and current() != '\n') {
+            step();
+        }
+        return next();
+    }
+    if (ch == '/') {
+        step();
+        if (current() == '/') {
+            while (not done() and current() != '\n') {
+                step();
+            }
+            return next();
+        }
+        return error_token(pos, "'/' not implemented");
+    }
+    if (ch == '-') {
+        step();
+        if (not done() and current() == '>') {
+            step();
+            return token(TokenType::MinusLt, pos);
+        }
+        return token(TokenType::Minus, pos);
+    }
+    if (ch == ':') {
+        step();
+        if (current() == ':') {
+            step();
+            return token(TokenType::ColonColon, pos);
+        }
+        return token(TokenType::Colon, pos);
+    }
+    switch (ch) {
+        case '(':
+            return single_token(TokenType::LParen, pos);
+        case ')':
+            return single_token(TokenType::RParen, pos);
+        case '{':
+            return single_token(TokenType::LBrace, pos);
+        case '}':
+            return single_token(TokenType::RBrace, pos);
+        case '[':
+            return single_token(TokenType::LBracket, pos);
+        case ']':
+            return single_token(TokenType::RBracket, pos);
+        case '.':
+            return single_token(TokenType::Dot, pos);
+        case ',':
+            return single_token(TokenType::Comma, pos);
+        case ';':
+            return single_token(TokenType::Semicolon, pos);
+    }
+    step();
+    return error_token(pos, "unrecognized character");
+}
+
+auto Lexer::populate_keyword_map()
+{
+    this->keyword_map["error"] = TokenType::Error;
+    this->keyword_map["eof"] = TokenType::Eof;
+    this->keyword_map["if"] = TokenType::If;
+    this->keyword_map["else"] = TokenType::Else;
+    this->keyword_map["return"] = TokenType::Return;
+    this->keyword_map["public"] = TokenType::Public;
+    this->keyword_map["private"] = TokenType::Private;
+    this->keyword_map["class"] = TokenType::Class;
+    this->keyword_map["derivable"] = TokenType::Derivable;
+    this->keyword_map["derives"] = TokenType::Derives;
+    this->keyword_map["enumeration"] = TokenType::Enumeration;
+    this->keyword_map["associate"] = TokenType::Associate;
+    this->keyword_map["attribute"] = TokenType::Attribute;
+    this->keyword_map["operation"] = TokenType::Operation;
+    this->keyword_map["state_machine"] = TokenType::StateMachine;
+    this->keyword_map["transition"] = TokenType::Transition;
+    this->keyword_map["initial"] = TokenType::Initial;
+    this->keyword_map["final"] = TokenType::Final;
+    this->keyword_map["entry"] = TokenType::Entry;
+    this->keyword_map["exit"] = TokenType::Exit;
+}
diff --git a/parser.hpp b/parser.hpp
new file mode 100644
index 0000000..02d6964
--- /dev/null
+++ b/parser.hpp
@@ -0,0 +1,142 @@
+#pragma once
+
+#include <cstdint>
+#include <fstream>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+namespace stela {
+
+struct Pos {
+    size_t index;
+    int64_t line;
+    int64_t col;
+};
+
+struct Error {
+    Pos pos;
+    std::string message;
+};
+
+enum class TokenType {
+    Error,
+    Eof,
+    If,
+    Else,
+    Return,
+    Public,
+    Private,
+    Class,
+    Derivable,
+    Derives,
+    Enumeration,
+    Associate,
+    Attribute,
+    Operation,
+    StateMachine,
+    Transition,
+    Initial,
+    Final,
+    Entry,
+    Exit,
+    LParen,
+    RParen,
+    LBrace,
+    RBrace,
+    LBracket,
+    RBracket,
+    Dot,
+    Comma,
+    Semicolon,
+    Colon,
+    ColonColon,
+    Minus,
+    MinusLt,
+    Equal,
+    Id,
+    Int,
+};
+
+struct Token {
+    TokenType type;
+    Pos pos;
+    uint64_t id;
+};
+
+class Lexer {
+public:
+    Lexer(std::ifstream& file, std::vector<Error>& errors)
+        : file(&file)
+        , current_char(file.get())
+        , errors(&errors)
+    { }
+
+    auto next() -> Token;
+
+private:
+    inline auto step()
+    {
+        if (this->current_char == EOF) {
+            this->eof_reached = true;
+            return;
+        }
+        if (this->current_char == '\n') {
+            this->line += 1;
+            this->col = 1;
+        } else {
+            this->col += 1;
+        }
+        this->current_char = this->file->get();
+        this->index += 1;
+    }
+
+    inline auto single_token(TokenType type, Pos pos) -> Token
+    {
+        step();
+        return token(type, pos);
+    }
+    inline auto error_token(Pos pos, std::string message) const -> Token
+    {
+        this->errors->push_back(Error { pos, message });
+        return token(TokenType::Error, pos);
+    }
+    inline auto token(TokenType type, Pos pos) const -> Token
+    {
+        return Token { type, pos, 0 };
+    }
+    inline auto pos() const -> Pos
+    {
+        return Pos {
+            .index = this->index,
+            .line = this->line,
+            .col = this->col,
+        };
+    }
+
+    inline auto done() const -> bool { return this->eof_reached; }
+    inline auto current() const -> char
+    {
+        return static_cast<char>(this->current_char);
+    }
+
+    auto populate_keyword_map();
+
+    bool eof_reached = false;
+
+    size_t index = 0;
+    int64_t line = 1;
+    int64_t col = 1;
+
+    std::ifstream* file;
+    int current_char;
+
+    std::unordered_map<std::string, TokenType> keyword_map {};
+
+    std::vector<std::string> symbol_values {};
+    std::vector<int64_t> int_values {};
+
+    std::vector<Error>* errors;
+};
+
+}