diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 479f8d2..c716c96 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -36,6 +36,8 @@ PRIVATE
     yycc/carton/clap/summary.cpp
     yycc/carton/clap/application.cpp
     yycc/carton/clap/manual.cpp
+    yycc/carton/clap/parser.cpp
+    yycc/carton/clap/resolver.cpp
 )
 target_sources(YYCCommonplace 
 PUBLIC
@@ -97,6 +99,8 @@ FILES
     yycc/carton/clap/application.hpp
     yycc/carton/clap/manual.hpp
     yycc/carton/clap/validator.hpp
+    yycc/carton/clap/parser.hpp
+    yycc/carton/clap/resolver.hpp
     yycc/carton/fft.hpp
 )
 # Setup header infomations
diff --git a/src/yycc/carton/clap/parser.cpp b/src/yycc/carton/clap/parser.cpp
new file mode 100644
index 0000000..4102d21
--- /dev/null
+++ b/src/yycc/carton/clap/parser.cpp
@@ -0,0 +1,3 @@
+#include "parser.hpp"
+
+namespace yycc::carton::clap::parser {}
diff --git a/src/yycc/carton/clap/parser.hpp b/src/yycc/carton/clap/parser.hpp
new file mode 100644
index 0000000..9446226
--- /dev/null
+++ b/src/yycc/carton/clap/parser.hpp
@@ -0,0 +1,5 @@
+#pragma once
+
+namespace yycc::carton::clap::parser {
+
+}
diff --git a/src/yycc/carton/clap/resolver.cpp b/src/yycc/carton/clap/resolver.cpp
new file mode 100644
index 0000000..6bfd614
--- /dev/null
+++ b/src/yycc/carton/clap/resolver.cpp
@@ -0,0 +1,81 @@
+#include "resolver.hpp"
+#include "types.hpp"
+#include <string_view>
+
+#define TYPES ::yycc::carton::clap::types
+
+namespace yycc::carton::clap::resolver {
+
+#pragma region Misc
+
+    /// @brief The states of parser internal state machine.
+    enum class ParserState {
+        Normal,       ///< Normal state. Expect an option.
+        WaitingValue, ///< Waiting an associated value.
+    };
+    /// @brief The state machine context prepared for parser.
+    struct ParserContext {
+        ParserContext() : state(ParserState::Normal), opt_waiting(std::nullopt) {}
+        YYCC_DEFAULT_COPY_MOVE(ParserContext)
+
+        ParserState state;                       ///< Current state.
+        std::optional<TYPES::Token> opt_waiting; ///< The token to the option waiting for associated value.
+    };
+
+    /// @brief The kind of argument.
+    enum class ArgumentKind { LongName, ShortName, Value };
+    /// @brief Representing a classified argument.
+    struct ClassifiedArgument {
+        ClassifiedArgument(const std::u8string_view& arg) {
+            if (arg.starts_with(TYPES::DOUBLE_DASH)) {
+                kind = ArgumentKind::LongName;
+                content = arg.substr(TYPES::DOUBLE_DASH.length());
+            } else if (arg.starts_with(TYPES::DASH)) {
+                kind = ArgumentKind::ShortName;
+                content = arg.substr(TYPES::DASH.length());
+            } else {
+                kind = ArgumentKind::Value;
+                content = arg;
+            }
+        }
+        YYCC_DEFAULT_COPY_MOVE(ClassifiedArgument)
+
+        /// @brief The kind of argument.
+        ArgumentKind kind;
+        /**
+         * @brief The data of argument.
+         * @details For long and short name, it is the body of option, the words removing any leading dash.
+         * For value, it just the value self.
+         */
+        std::u8string_view content;
+    };
+
+#pragma endregion
+
+#pragma region Core
+
+#pragma endregion
+
+#pragma region Parser Class
+
+    Parser::Parser(const NS_YYCC_CLAP_APPLICATION::Application& app) {}
+
+    Parser::~Parser() {}
+
+    bool Parser::has_option(TYPES::Token token) const {
+        // TODO:
+        return false;
+    }
+
+    TYPES::ClapResult<bool> Parser::get_flag_option(TYPES::Token token) const {
+        // TODO:
+        return TYPES::ClapResult<bool>();
+    }
+
+    TYPES::ClapResult<std::u8string_view> Parser::get_raw_value_option(TYPES::Token token) const {
+        // TODO:
+        return TYPES::ClapResult<std::u8string_view>();
+    }
+#pragma endregion
+
+} // namespace yycc::carton::clap::resolver
diff --git a/src/yycc/carton/clap/resolver.hpp b/src/yycc/carton/clap/resolver.hpp
new file mode 100644
index 0000000..50488b8
--- /dev/null
+++ b/src/yycc/carton/clap/resolver.hpp
@@ -0,0 +1,53 @@
+#pragma once
+#include "../../macro/class_copy_move.hpp"
+#include "application.hpp"
+#include "validator.hpp"
+#include <map>
+#include <optional>
+#include <string>
+
+#define NS_YYCC_CLAP_TYPES ::yycc::carton::clap::types
+#define NS_YYCC_CLAP_APPLICATION ::yycc::carton::clap::application
+#define NS_YYCC_CLAP_VALIDATOR ::yycc::carton::clap::validator
+
+namespace yycc::carton::clap::resolver {
+
+    class Parser {
+    public:
+        Parser(const NS_YYCC_CLAP_APPLICATION::Application& app);
+        ~Parser();
+        YYCC_DEFAULT_COPY_MOVE(Parser)
+
+    private:
+        NS_YYCC_CLAP_TYPES::ClapResult<std::u8string_view> get_raw_value_option(NS_YYCC_CLAP_TYPES::Token token) const;
+
+    public:
+        bool has_option(NS_YYCC_CLAP_TYPES::Token token) const;
+        NS_YYCC_CLAP_TYPES::ClapResult<bool> get_flag_option(NS_YYCC_CLAP_TYPES::Token token) const;
+        template<NS_YYCC_CLAP_VALIDATOR::Validator T>
+        NS_YYCC_CLAP_TYPES::ClapResult<NS_YYCC_CLAP_VALIDATOR::ValidatorReturnType<T>> get_value_option(
+            NS_YYCC_CLAP_TYPES::Token token) const {
+            auto raw_value = this->get_raw_value_option(token);
+            if (raw_value.has_value()) {
+                T validator{};
+                auto value = validator.validate(raw_value.value());
+                if (value.has_value()) return value.value();
+                else return std::unexpected(NS_YYCC_CLAP_TYPES::ClapError::BadCast);
+            } else {
+                return std::unexpected(raw_value.error())
+            }
+        }
+
+    private:
+        /**
+         * @brief All captured commandline argument.
+         * @details Key is the token to already registered option.
+         * Value is the associated value for key token.
+         * If it is no-value option, the value will be \c std::nullopt.
+         */
+        std::map<NS_YYCC_CLAP_TYPES::Token, std::optional<std::u8string>> values;
+    };
+
+} // namespace yycc::carton::clap::resolver
+
+#undef NS_YYCC_CLAP_TYPES
diff --git a/src/yycc/carton/clap/types.hpp b/src/yycc/carton/clap/types.hpp
index 0d6f1b8..edaa891 100644
--- a/src/yycc/carton/clap/types.hpp
+++ b/src/yycc/carton/clap/types.hpp
@@ -6,7 +6,12 @@ namespace yycc::carton::clap::types {
 
     /// @brief All possible error kind occurs in this module.
     enum class ClapError {
-
+        InvalidName,      ///< When parsing commandline argument, given option name is invalid.
+        DuplicatedAssign, ///< When parsing commandline argument, multiple assign for a single option.
+        UnexpectedValue,  ///< When parsing commandline argument, reach associated value unexpected.
+        LostValue,        ///< When parsing commandline argument, fail to find associated value.
+        NotCaptured,      ///< When fetching option or variable, given option or variable is not captured.
+        BadCast           ///< When fetching option or variable, the content of given option or variable can not be cast into expected type.
     };
 
     /// @brief The result type used in this module.
diff --git a/src/yycc/carton/clap/validator.hpp b/src/yycc/carton/clap/validator.hpp
index 0946b14..d5ca76d 100644
--- a/src/yycc/carton/clap/validator.hpp
+++ b/src/yycc/carton/clap/validator.hpp
@@ -19,17 +19,23 @@ namespace yycc::carton::clap::validator {
      * And, it also should have an member function called "validate"
      * which receive <TT>const std::string_view&</TT> as its only argument,
      * and return <TT>std::optional<ReturnType></TT> as result.
-     * If this \t std::optional is empty, it means that there is some error occurs when validating,
+     * If this \c std::optional is empty, it means that there is some error occurs when validating,
      * otherwise, it is the validated value.
+     * 
+     * Finally, it must can be default initialized.
      */
     template<typename T>
-    concept Validator = requires(const T& t, const std::u8string_view& sv) {
+    concept Validator = std::default_initializable<T> && requires(const T& t, const std::u8string_view& sv) {
         // Check whether there is T::ReturnType type
         typename T::ReturnType;
         // Check whether there is "validate" member function and it has correct signature.
         { t.validate(sv) } -> std::same_as<std::optional<typename T::ReturnType>>;
     };
 
+    /// @brief A convenient alias to the return type of validator.
+    template<Validator T>
+    using ValidatorReturnType = T::ReturnType;
+
     template<std::integral T, auto TMin = std::numeric_limits<T>::min(), auto TMax = std::numeric_limits<T>::max()>
     struct IntegralValidator {
         static_assert(TMin <= TMax);