diff --git a/compiler/compiler.cc b/compiler/compiler.cc
index 4aca13f..6a487fd 100644
--- a/compiler/compiler.cc
+++ b/compiler/compiler.cc
@@ -1 +1,61 @@
-#include "compiler/compiler.h"
\ No newline at end of file
+// Copyright 2024 AQ authors, All Rights Reserved.
+// This program is licensed under the AQ License. You can find the AQ license in
+// the root directory.
+
+#include "compiler/compiler.h"
+
+#include <chrono>
+#include <cstdint>
+#include <cstring>
+#include <fstream>
+#include <iostream>
+#include <vector>
+
+#include "debugger/debugger.h"
+#include "compiler/lexer/lexer.h"
+#include "compiler/lexer/token.h"
+
+namespace Aq {
+Compiler::Compiler() = default;
+Compiler::~Compiler() = default;
+
+int Compiler::CompileFile(const char* filename) {
+  // TODO: Waiting for improvements.
+  auto start = std::chrono::high_resolution_clock::now();
+  std::ifstream file;
+  file.open(filename);
+  if (!file.is_open()) {
+    Aq::Debugger error_info(Aq::Debugger::Level::ERROR, "Aq::Main",
+                            "Main_ReadFileError", "Can't open file.", nullptr);
+    return -1;
+  }
+
+  std::vector<char> code;
+  char ch;
+  while (file.get(ch)) {
+    code.push_back(ch);
+  }
+  code.push_back('\0');
+  file.close();
+  Lexer lexer(code.data(), code.size() - 1);
+  Token token;
+  while (true) {
+    int return_value = lexer.LexToken(token);
+    if (token.length == 0) {
+      std::cout << "END OF THE CODE.";
+    } else {
+      std::cout << std::string(token.location, token.length) << std::endl;
+    }
+    if (lexer.IsReadEnd()) {
+      break;
+    }
+  }
+  auto end = std::chrono::high_resolution_clock::now();
+  auto duration_in_milliseconds =
+      std::chrono::duration_cast<std::chrono::milliseconds>(end - start);
+  double duration_in_seconds =
+      static_cast<double>(duration_in_milliseconds.count()) / 1000.0;
+  std::cout << "Execution time: " << duration_in_seconds << " seconds.\n";
+  return 0;
+}
+}  // namespace Aq
\ No newline at end of file
diff --git a/compiler/compiler.h b/compiler/compiler.h
index ffba818..cc8ac1b 100644
--- a/compiler/compiler.h
+++ b/compiler/compiler.h
@@ -1,10 +1,26 @@
+// Copyright 2024 AQ authors, All Rights Reserved.
+// This program is licensed under the AQ License. You can find the AQ license in
+// the root directory.
+
 #ifndef AQ_COMPILE_COMPILE_H_
 #define AQ_COMPILE_COMPILE_H_
 
 namespace Aq {
-namespace Compiler {
-extern int CompileFile(const char* filename);
-}
+class Compiler {
+ public:
+  Compiler();
+  ~Compiler();
+
+  int CompileFile(const char* filename);
+
+ private:
+  class Lexer;
+  struct Token;
+  template <typename T>
+  class LexMap;
+  class TokenMap;
+  class Parser;
+};
 }  // namespace Aq
 
 #endif  // AQ_COMPILE_H_
\ No newline at end of file
diff --git a/compiler/lexer/lex_map.h b/compiler/lexer/lex_map.h
index 93c642c..887b425 100644
--- a/compiler/lexer/lex_map.h
+++ b/compiler/lexer/lex_map.h
@@ -9,14 +9,14 @@
 #include <cstring>
 #include <limits>
 
+#include "compiler/compiler.h"
 #include "debugger/debugger.h"
 
 namespace Aq {
-namespace Compiler {
 // A hash table for the lexer. Used to find special definitions such as compiler
 // keywords.
 template <typename T>
-class LexMap {
+class Compiler::LexMap {
  public:
   // Construct a LexMap class, and the default hash table memory size is 1024.
   // Do not modify it unless necessary.
@@ -196,7 +196,5 @@ class LexMap {
     return 0;
   };
 };
-}  // namespace Compiler
 }  // namespace Aq
-
 #endif
\ No newline at end of file
diff --git a/compiler/lexer/lexer.cc b/compiler/lexer/lexer.cc
index 391873c..1e60174 100644
--- a/compiler/lexer/lexer.cc
+++ b/compiler/lexer/lexer.cc
@@ -6,12 +6,12 @@
 
 #include <string>
 
+#include "compiler/compiler.h"
 #include "compiler/lexer/token.h"
 #include "debugger/debugger.h"
 
 namespace Aq {
-namespace Compiler {
-bool Lexer::IsReadEnd() const {
+bool Compiler::Lexer::IsReadEnd() const {
   if (buffer_ptr_ >= buffer_end_) {
     return true;
   } else {
@@ -19,7 +19,7 @@ bool Lexer::IsReadEnd() const {
   }
 }
 
-int Lexer::LexToken(Token& return_token) {
+int Compiler::Lexer::LexToken(Token& return_token) {
   // Set the return token type to start.
   return_token.type = Token::Type::START;
 
@@ -415,5 +415,4 @@ int Lexer::LexToken(Token& return_token) {
     return 0;
   }
 }
-}  // namespace Compiler
 }  // namespace Aq
\ No newline at end of file
diff --git a/compiler/lexer/lexer.h b/compiler/lexer/lexer.h
index 8fbb22e..21347e8 100644
--- a/compiler/lexer/lexer.h
+++ b/compiler/lexer/lexer.h
@@ -7,11 +7,11 @@
 
 #include <cstddef>
 
+#include "compiler/compiler.h"
 #include "compiler/lexer/token.h"
 
 namespace Aq {
-namespace Compiler {
-class Lexer {
+class Compiler::Lexer {
  public:
   // Initialize the Lexer class and store |source_code| to |buffer_ptr_|.
   Lexer(char* source_code, size_t length)
@@ -35,7 +35,6 @@ class Lexer {
   char* buffer_end_;
   TokenMap token_map_;
 };
-}  // namespace Compiler
 }  // namespace Aq
 
 #endif
\ No newline at end of file
diff --git a/compiler/lexer/test.cc b/compiler/lexer/test.cc
index ca11cc7..c41d858 100644
--- a/compiler/lexer/test.cc
+++ b/compiler/lexer/test.cc
@@ -2,63 +2,10 @@
 // This program is licensed under the AQ License. You can find the AQ license in
 // the root directory.
 
-#include <chrono>
-#include <cstdint>
-#include <cstring>
-#include <fstream>
-#include <iostream>
-#include <vector>
-
-#include "aq/aq.h"
-#include "compiler/lexer/lex_map.h"
-#include "compiler/lexer/lexer.h"
-#include "compiler/lexer/token.h"
-#include "debugger/debugger.h"
-
-int LexerTest(int argc, char* argv[]) {
-  auto start = std::chrono::high_resolution_clock::now();
-  std::ifstream file;
-  const char* filename = argv[1];
-  file.open(filename);
-  if (!file.is_open()) {
-    Aq::Debugger error_info(Aq::Debugger::Level::ERROR, "Aq::Main",
-                            "Main_ReadFileError", "Can't open file.", nullptr);
-    return -1;
-  }
-
-  std::vector<char> code;
-  char ch;
-  while (file.get(ch)) {
-    code.push_back(ch);
-  }
-  code.push_back('\0');
-  file.close();
-  Aq::Compiler::Lexer lexer(code.data(), code.size() - 1);
-  Aq::Compiler::Token token;
-  while (true) {
-    int return_value = lexer.LexToken(token);
-    if (token.length == 0) {
-      std::cout << "END OF THE CODE.";
-    } else {
-      std::cout << std::string(token.location, token.length) << std::endl;
-    }
-    if (lexer.IsReadEnd()) {
-      break;
-    }
-  }
-  auto end = std::chrono::high_resolution_clock::now();
-  auto duration_in_milliseconds =
-      std::chrono::duration_cast<std::chrono::milliseconds>(end - start);
-  double duration_in_seconds =
-      static_cast<double>(duration_in_milliseconds.count()) / 1000.0;
-  std::cout << "Execution time: " << duration_in_seconds << " seconds.\n";
-  return 0;
-}
-
-int LexMapTest(int argc, char* argv[]) { return 0; }
+#include "compiler/compiler.h"
 
 int main(int argc, char* argv[]) {
-  LexerTest(argc, argv);
-  LexMapTest(argc, argv);
+  Aq::Compiler compiler;
+  compiler.CompileFile(argv[1]);
   return 0;
 }
diff --git a/compiler/lexer/token.cc b/compiler/lexer/token.cc
index cca4cf4..fbe7b6f 100644
--- a/compiler/lexer/token.cc
+++ b/compiler/lexer/token.cc
@@ -4,13 +4,13 @@
 
 #include "compiler/lexer/token.h"
 
+#include "compiler/compiler.h"
 #include "compiler/lexer/lex_map.h"
 #include "debugger/debugger.h"
 
 namespace Aq {
-namespace Compiler {
-Token::Token() = default;
-Token::~Token() {
+Compiler::Token::Token() = default;
+Compiler::Token::~Token() {
   if (type == Type::NUMBER) {
     delete[] value.Number;
   } else if (type == Type::IDENTIFIER) {
@@ -22,7 +22,7 @@ Token::~Token() {
   }
 }
 
-TokenMap::TokenMap() {
+Compiler::TokenMap::TokenMap() {
   keyword_map.Insert("auto", Token::KeywordType::Auto);
   keyword_map.Insert("and", Token::KeywordType::And);
   keyword_map.Insert("bitand", Token::KeywordType::Bitand);
@@ -143,13 +143,12 @@ TokenMap::TokenMap() {
   operator_map.Insert(">>>", Token::OperatorType::greatergreatergreater);
   operator_map.Insert("^^", Token::OperatorType::caretcaret);
 }
-TokenMap::~TokenMap() = default;
+Compiler::TokenMap::~TokenMap() = default;
 
-Token::KeywordType TokenMap::GetKeywordValue(const char* keyword) {
+Compiler::Token::KeywordType Compiler::TokenMap::GetKeywordValue(const char* keyword) {
   return keyword_map.Find(keyword);
 }
-Token::OperatorType TokenMap::GetOperatorValue(const char* _operator) {
+Compiler::Token::OperatorType Compiler::TokenMap::GetOperatorValue(const char* _operator) {
   return operator_map.Find(_operator);
 }
-}  // namespace Compiler
 }  // namespace Aq
\ No newline at end of file
diff --git a/compiler/lexer/token.h b/compiler/lexer/token.h
index 00a44a1..b19c657 100644
--- a/compiler/lexer/token.h
+++ b/compiler/lexer/token.h
@@ -5,11 +5,11 @@
 #ifndef AQ_COMPILER_LEXER_TOKEN_H_
 #define AQ_COMPILER_LEXER_TOKEN_H_
 
+#include "compiler/compiler.h"
 #include "compiler/lexer/lex_map.h"
 
 namespace Aq {
-namespace Compiler {
-struct Token {
+struct Compiler::Token {
   enum class Type {
     START,
     KEYWORD,
@@ -168,7 +168,7 @@ struct Token {
   Token& operator=(Token&&) noexcept = default;
 };
 
-class TokenMap {
+class Compiler::TokenMap {
  public:
   TokenMap();
   ~TokenMap();
@@ -185,7 +185,5 @@ class TokenMap {
   LexMap<Token::KeywordType> keyword_map;
   LexMap<Token::OperatorType> operator_map;
 };
-
-}  // namespace Compiler
 }  // namespace Aq
 #endif
\ No newline at end of file