diff --git a/CMakeLists.txt b/CMakeLists.txt
index 14cea4c..6fdf434 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -86,10 +86,6 @@ set(CMAKE_CXX_FLAGS_DEBUG "-DSPDLOG_ACTIVE_LEVEL=SPDLOG_LEVEL_TRACE")
 include(./cmake/PFL.cmake)
 
 set(OCPPI_LIBS common runtime cli)
-
-set(PFL_ENABLE_TESTING ${OCPPI_ENABLE_TESTING})
-set(PFL_BUILD_EXAMPLES ${OCPPI_BUILD_EXAMPLES})
-
-foreach(LIB ${OCPPI_LIBS})
-  pfl_add_subdirectory(TARGET_PREFIX ocppi libs/${LIB})
-endforeach()
+pfl_init(ENABLE_TESTING ${OCPPI_ENABLE_TESTING} BUILD_EXAMPLES
+         ${OCPPI_BUILD_EXAMPLES})
+pfl_add_libraries(${OCPPI_LIBS})
diff --git a/cmake/PFL.cmake b/cmake/PFL.cmake
index ba3b46a..28dc125 100644
--- a/cmake/PFL.cmake
+++ b/cmake/PFL.cmake
@@ -1,366 +1,366 @@
-get_property (
-        PFL_INITIALIZED GLOBAL ""
-        PROPERTY
-                PFL_INITIALIZED
-        SET
-)
+# SPDX-FileCopyrightText: 2023 Chen Linxuan <me@black-desk.cn>
+#
+# SPDX-License-Identifier: LGPL-3.0-or-later
+
+cmake_minimum_required(VERSION 3.23 FATAL_ERROR)
+
+get_property(
+  PFL_INITIALIZED GLOBAL ""
+  PROPERTY PFL_INITIALIZED
+  SET)
 if(PFL_INITIALIZED)
-        return ()
+  return()
 endif()
 
-function(pfl_add_subdirectory)
-        cmake_parse_arguments (
-                PFL_ADD_SUBDIRECTORY
-                ""
-                "TARGET_PREFIX"
-                ""
-                ${ARGN}
-        )
-        set (PFL_PREFIX ${PFL_ADD_SUBDIRECTORY_TARGET_PREFIX})
-        add_subdirectory (${PFL_ADD_SUBDIRECTORY_UNPARSED_ARGUMENTS})
+set_property(GLOBAL PROPERTY PFL_INITIALIZED true)
+
+# You should call this function in your top level CMakeLists.txt to tell
+# PFL.cmake some global settings about your project.
+#
+# ENABLE_TESTING bool: Whether to build tests for libraries or not.
+#
+# BUILD_EXAMPLES bool: Whether to build examples for libraries or not.
+#
+# EXTERNALS list of string: External projects to build.
+function(pfl_init)
+  cmake_parse_arguments(PFL_INIT "" "ENABLE_TESTING;BUILD_EXAMPLES" "EXTERNALS"
+                        ${ARGN})
+  set(PFL_ENABLE_TESTING
+      ${PFL_INIT_ENABLE_TESTING}
+      PARENT_SCOPE)
+  set(PFL_BUILD_EXAMPLES
+      ${PFL_INIT_BUILD_EXAMPLES}
+      PARENT_SCOPE)
+  foreach(EXTERNAL ${PFL_INIT_EXTERNALS})
+    add_subdirectory(${CMAKE_CURRENT_LIST_DIR}/external/${EXTERNAL})
+  endforeach()
 endfunction()
 
-function(pfl_configure_files)
-        cmake_parse_arguments (
-                PFL_CONFIGURE_FILES
-                ""
-                "HEADERS;SOURCES"
-                "INS"
-                ${ARGN}
-        )
-
-        foreach(IN_FILE ${PFL_CONFIGURE_FILES_INS})
-                string (
-                        REGEX
-                        REPLACE
-                                "\.in$" "" OUT_FILE ${IN_FILE}
-                )
-
-                configure_file (
-                        ${IN_FILE} ${CMAKE_CURRENT_BINARY_DIR}/${OUT_FILE}
-                        @ONLY
-                )
-
-                if(OUT_FILE MATCHES "^include\/.*\.h(h|pp)?$")
-                        list (
-                                APPEND ${PFL_CONFIGURE_FILES_HEADERS}
-                                ${CMAKE_CURRENT_BINARY_DIR}/${OUT_FILE}
-                        )
-                elseif(OUT_FILE MATCHES "^src\/.*\.(h(h|pp)?|cpp)$")
-                        list (
-                                APPEND ${PFL_CONFIGURE_FILES_SOURCES}
-                                ${CMAKE_CURRENT_BINARY_DIR}/${OUT_FILE}
-                        )
-                else()
-                        # TODO: add other files later
-                endif()
-        endforeach()
-
-        set (
-                ${PFL_CONFIGURE_FILES_HEADERS}
-                ${${PFL_CONFIGURE_FILES_HEADERS}}
-                PARENT_SCOPE
-        )
-
-        set (
-                ${PFL_CONFIGURE_FILES_SOURCES}
-                ${${PFL_CONFIGURE_FILES_SOURCES}}
-                PARENT_SCOPE
-        )
+function(__pfl_configure_files)
+  cmake_parse_arguments(PFL_CONFIGURE_FILES "" "HEADERS;SOURCES" "INS" ${ARGN})
+
+  foreach(IN_FILE ${PFL_CONFIGURE_FILES_INS})
+    string(REGEX REPLACE "\.in$" "" OUT_FILE ${IN_FILE})
+
+    configure_file(${IN_FILE} ${CMAKE_CURRENT_BINARY_DIR}/${OUT_FILE} @ONLY)
+
+    if(OUT_FILE MATCHES "^include\/.*\.h(h|pp)?$")
+      list(APPEND ${PFL_CONFIGURE_FILES_HEADERS}
+           ${CMAKE_CURRENT_BINARY_DIR}/${OUT_FILE})
+    elseif(OUT_FILE MATCHES "^src\/.*\.(h(h|pp)?|cpp)$")
+      list(APPEND ${PFL_CONFIGURE_FILES_SOURCES}
+           ${CMAKE_CURRENT_BINARY_DIR}/${OUT_FILE})
+    else()
+      # TODO: add other files later
+    endif()
+  endforeach()
+
+  set(${PFL_CONFIGURE_FILES_HEADERS}
+      ${${PFL_CONFIGURE_FILES_HEADERS}}
+      PARENT_SCOPE)
+
+  set(${PFL_CONFIGURE_FILES_SOURCES}
+      ${${PFL_CONFIGURE_FILES_SOURCES}}
+      PARENT_SCOPE)
 endfunction()
 
+# This function is used to add libraries under the `libs` directory. It just
+# takes in a string list contains the directory name under `libs`.
+function(pfl_add_libraries)
+  message(
+    STATUS
+      "PFL:${PFL_MESSAGE_INDENT} Adding libraries at ${CMAKE_CURRENT_SOURCE_DIR}"
+  )
+  set(PFL_MESSAGE_INDENT "${PFL_MESSAGE_INDENT}  ")
+
+  cmake_path(GET CMAKE_CURRENT_SOURCE_DIR FILENAME TARGET_DIR_NAME)
+  string(REPLACE " " "_" TARGET_NAME "${TARGET_DIR_NAME}")
+
+  if(PFL_PREFIX)
+    set(PFL_PREFIX "${PFL_PREFIX}::${TARGET_DIR_NAME}")
+  else()
+    set(PFL_PREFIX "${TARGET_DIR_NAME}")
+  endif()
+
+  foreach(LIB ${ARGN})
+    add_subdirectory(libs/${LIB})
+  endforeach()
+endfunction()
+
+# This function is used to add a library.
+#
+# HEADER_ONLY option: Whether this library is a header only library.
+#
+# INTERNAL option: Whether this library is a internal library.
+#
+# OUTPUT_NAME string: The output file name of this library.
+#
+# SOVERSION string: The soversion of this library.
+#
+# VERSION string: The version of this library.
+#
+# TYPE [STATIC | SHARED]: The type of this library.
+#
+# INS list of string: .in files to configure, it use @ONLY to configure_file.
+#
+# SOURCE list of string: file names of source and private headers.
+#
+# HEADERS list of string: file names of public headers.
+#
+# LINK_LIBRARIES: arguments passed to target_link_libraries.
+#
+# COMPILE_FEATURES: arguments target_compile_features.
+#
+# APPS: list of string: directory names under "apps" directory.
+#
+# EXAMPLES: list of string: directory names under "examples" directory.
 function(pfl_add_library)
-        message (
-                STATUS
-                        "PFL: Building library at"
-                        "${CMAKE_CURRENT_SOURCE_DIR} ..."
-        )
-
-        cmake_parse_arguments (
-                PFL_ADD_LIBRARY
-                "HEADER_ONLY;INTERNAL;NO_INSTALL"
-                "OUTPUT_NAME;SOVERSION;VERSION;TYPE"
-                "INS;SOURCES;HEADERS;LINK_LIBRARIES;COMPILE_FEATURES;APPS;EXAMPLES"
-                ${ARGN}
-        )
-
-        cmake_path (
-                GET
-                CMAKE_CURRENT_SOURCE_DIR
-                FILENAME
-                TARGET_DIR_NAME
-        )
-
-        string (
-                REPLACE
-                        " " "_" TARGET_NAME "${TARGET_DIR_NAME}"
-        )
-
-        string (
-                REPLACE
-                        "::" "__" TARGET_PREFIX "${PFL_PREFIX}"
-        )
-
-        if(TARGET_PREFIX)
-                set (TARGET_NAME "${TARGET_PREFIX}__${TARGET_NAME}")
-        endif()
-
-        string (
-                REPLACE
-                        "__" "::" TARGET_EXPORT_NAME "${TARGET_NAME}"
-        )
-
-        message (
-                STATUS
-                        "PFL: Adding library ${TARGET_EXPORT_NAME} ..."
-        )
-
-        pfl_configure_files (
-                INS
-                ${PFL_ADD_LIBRARY_INS}
-                HEADERS
-                PFL_ADD_LIBRARY_HEADERS
-                SOURCES
-                PFL_ADD_LIBRARY_SOURCES
-        )
-
-        if(PFL_ADD_LIBRARY_HEADER_ONLY)
-                add_library ("${TARGET_NAME}" INTERFACE)
-                add_library ("${TARGET_NAME}__BUILD" ${PFL_ADD_LIBRARY_SOURCES})
-                target_link_libraries (
-                        "${TARGET_NAME}__BUILD" PUBLIC
-                                                        "${TARGET_NAME}"
-                )
-        else()
-                add_library (
-                        "${TARGET_NAME}" ${PFL_ADD_LIBRARY_TYPE}
-                                         ${PFL_ADD_LIBRARY_SOURCES}
-                )
-        endif()
-
-        if(PFL_ADD_LIBRARY_SOVERSION AND NOT PFL_ADD_LIBRARY_HEADER_ONLY)
-                set_target_properties (
-                        "${TARGET_NAME}"
-                        PROPERTIES
-                                SOVERSION ${PFL_ADD_LIBRARY_SOVERSION}
-                )
-        endif()
-
-        add_library ("${TARGET_EXPORT_NAME}" ALIAS "${TARGET_NAME}")
-
-        set_target_properties (
-                "${TARGET_NAME}" PROPERTIES
-                                         EXPORT_NAME ${TARGET_DIR_NAME}
-        )
-
-        if(PFL_ADD_LIBRARY_OUTPUT_NAME)
-                set_target_properties (
-                        "${TARGET_NAME}"
-                        PROPERTIES
-                                OUTPUT_NAME ${PFL_ADD_LIBRARY_OUTPUT_NAME}
-                )
-        endif()
-
-        target_sources (
-                ${TARGET_NAME}
-                PUBLIC
-                        FILE_SET HEADERS BASE_DIRS include
-                        ${CMAKE_CURRENT_BINARY_DIR}/include FILES
-                        ${PFL_ADD_LIBRARY_HEADERS}
-        )
-
-        if(NOT PFL_ADD_LIBRARY_HEADER_ONLY)
-                target_include_directories (
-                        ${TARGET_NAME}
-                        PRIVATE
-                                src ${CMAKE_CURRENT_BINARY_DIR}/src
-                )
-        endif()
-
-        if(PFL_ADD_LIBRARY_LINK_LIBRARIES)
-                target_link_libraries (
-                        ${TARGET_NAME} ${PFL_ADD_LIBRARY_LINK_LIBRARIES}
-                )
-        endif()
-
-        if(PFL_ADD_LIBRARY_COMPILE_FEATURES)
-                target_compile_features (
-                        ${TARGET_NAME} ${PFL_ADD_LIBRARY_COMPILE_FEATURES}
-                )
-        endif()
-
-        if(NOT PFL_ADD_LIBRARY_NO_INSTALL AND NOT PFL_ADD_LIBRARY_INTERNAL)
-                include (GNUInstallDirs)
-
-                install (
-                        TARGETS
-                                "${TARGET_NAME}"
-                        EXPORT
-                                "${TARGET_NAME}"
-                        FILE_SET HEADERS
-                )
-
-                install (
-                        EXPORT
-                                "${TARGET_NAME}"
-                        DESTINATION
-                                ${CMAKE_INSTALL_LIBDIR}/cmake/${TARGET_NAME}
-                        FILE "${TARGET_NAME}.cmake"
-                        NAMESPACE
-                                ${PFL_PREFIX}::
-                )
-
-                if(EXISTS
-                   ${CMAKE_CURRENT_SOURCE_DIR}/misc/cmake/${TARGET_NAME}-config.cmake.in
-                )
-                        include (CMakePackageConfigHelpers)
-                        # This will be used to replace @PACKAGE_cmakeModulesDir@
-                        set (cmakeModulesDir cmake)
-
-                        configure_package_config_file (
-                                misc/cmake/${TARGET_NAME}-config.cmake.in
-                                misc/cmake/${TARGET_NAME}-config.cmake
-                                INSTALL_DESTINATION
-                                        ${CMAKE_INSTALL_LIBDIR}/cmake/${TARGET_NAME}
-                                PATH_VARS
-                                        cmakeModulesDir
-                                NO_SET_AND_CHECK_MACRO
-                                NO_CHECK_REQUIRED_COMPONENTS_MACRO
-                        )
-
-                        write_basic_package_version_file (
-                                ${CMAKE_CURRENT_BINARY_DIR}/misc/cmake/${TARGET_NAME}-config-version.cmake
-                                VERSION
-                                        ${PFL_ADD_LIBRARY_VERSION}
-                                COMPATIBILITY
-                                        SameMajorVersion
-                        )
-
-                        install (
-                                FILES
-                                        ${CMAKE_CURRENT_BINARY_DIR}/misc/cmake/${TARGET_NAME}-config.cmake
-                                        ${CMAKE_CURRENT_BINARY_DIR}/misc/cmake/${TARGET_NAME}-config-version.cmake
-                                DESTINATION
-                                        ${CMAKE_INSTALL_LIBDIR}/cmake/${TARGET_NAME}
-                        )
-                endif()
-        endif()
-
-        if(EXISTS tests AND PFL_ENABLE_TESTING)
-                add_subdirectory (tests)
-        endif()
-
-        if(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/examples"
-           AND PFL_ADD_LIBRARY_EXAMPLES
-           AND PFL_BUILD_EXAMPLES
-        )
-                foreach(EXAMPLE ${PFL_ADD_LIBRARY_EXAMPLES})
-                        add_subdirectory ("examples/${EXAMPLE}")
-                endforeach()
-        endif()
-
-        if(EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/apps" AND PFL_ADD_LIBRARY_APPS)
-                foreach(APP ${PFL_ADD_LIBRARY_APP})
-                        add_subdirectory ("${APP}")
-                endforeach()
-        endif()
+  cmake_parse_arguments(
+    PFL_ADD_LIBRARY "HEADER_ONLY;INTERNAL" "OUTPUT_NAME;SOVERSION;VERSION;TYPE"
+    "INS;SOURCES;HEADERS;LINK_LIBRARIES;COMPILE_FEATURES;APPS;EXAMPLES" ${ARGN})
+
+  cmake_path(GET CMAKE_CURRENT_SOURCE_DIR FILENAME TARGET_DIR_NAME)
+
+  string(REPLACE " " "_" TARGET_NAME "${TARGET_DIR_NAME}")
+
+  string(REPLACE "::" "__" TARGET_PREFIX "${PFL_PREFIX}")
+
+  if(TARGET_PREFIX)
+    set(TARGET_NAME "${TARGET_PREFIX}__${TARGET_NAME}")
+  endif()
+
+  string(REPLACE "__" "::" TARGET_EXPORT_NAME "${TARGET_NAME}")
+
+  message(
+    STATUS
+      "PFL:${PFL_MESSAGE_INDENT} Adding library ${TARGET_EXPORT_NAME} at ${CMAKE_CURRENT_SOURCE_DIR}"
+  )
+  set(PFL_MESSAGE_INDENT "${PFL_MESSAGE_INDENT}  ")
+
+  __pfl_configure_files(INS ${PFL_ADD_LIBRARY_INS} HEADERS
+                        PFL_ADD_LIBRARY_HEADERS SOURCES PFL_ADD_LIBRARY_SOURCES)
+
+  if(PFL_ADD_LIBRARY_HEADER_ONLY)
+    add_library("${TARGET_NAME}" INTERFACE)
+    add_library("${TARGET_NAME}__BUILD" ${PFL_ADD_LIBRARY_SOURCES})
+    target_link_libraries("${TARGET_NAME}__BUILD" PUBLIC "${TARGET_NAME}")
+  else()
+    add_library("${TARGET_NAME}" ${PFL_ADD_LIBRARY_TYPE}
+                                 ${PFL_ADD_LIBRARY_SOURCES})
+  endif()
+
+  if(PFL_ADD_LIBRARY_SOVERSION AND NOT PFL_ADD_LIBRARY_HEADER_ONLY)
+    set_target_properties("${TARGET_NAME}"
+                          PROPERTIES SOVERSION ${PFL_ADD_LIBRARY_SOVERSION})
+  endif()
+
+  if(NOT "${TARGET_EXPORT_NAME}" STREQUAL "${TARGET_NAME}")
+    add_library("${TARGET_EXPORT_NAME}" ALIAS "${TARGET_NAME}")
+  endif()
+
+  set_target_properties("${TARGET_NAME}" PROPERTIES EXPORT_NAME
+                                                    ${TARGET_DIR_NAME})
+
+  if(PFL_ADD_LIBRARY_OUTPUT_NAME)
+    set_target_properties("${TARGET_NAME}"
+                          PROPERTIES OUTPUT_NAME ${PFL_ADD_LIBRARY_OUTPUT_NAME})
+  endif()
+
+  target_sources(
+    ${TARGET_NAME}
+    PUBLIC FILE_SET
+           HEADERS
+           BASE_DIRS
+           include
+           ${CMAKE_CURRENT_BINARY_DIR}/include
+           FILES
+           ${PFL_ADD_LIBRARY_HEADERS})
+
+  if(NOT PFL_ADD_LIBRARY_HEADER_ONLY)
+    if(PFL_ADD_LIBRARY_INTERNAL)
+      target_include_directories(${TARGET_NAME}
+                                 PUBLIC src ${CMAKE_CURRENT_BINARY_DIR}/src)
+    else()
+      target_include_directories(${TARGET_NAME}
+                                 PRIVATE src ${CMAKE_CURRENT_BINARY_DIR}/src)
+    endif()
+  endif()
+
+  if(PFL_ADD_LIBRARY_LINK_LIBRARIES)
+    target_link_libraries(${TARGET_NAME} ${PFL_ADD_LIBRARY_LINK_LIBRARIES})
+  endif()
+
+  if(PFL_ADD_LIBRARY_COMPILE_FEATURES)
+    target_compile_features(${TARGET_NAME} ${PFL_ADD_LIBRARY_COMPILE_FEATURES})
+  endif()
+
+  if(NOT PFL_ADD_LIBRARY_INTERNAL)
+    include(GNUInstallDirs)
+
+    install(
+      TARGETS "${TARGET_NAME}"
+      EXPORT "${TARGET_NAME}"
+      FILE_SET HEADERS)
+
+    install(
+      EXPORT "${TARGET_NAME}"
+      DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${TARGET_NAME}
+      FILE "${TARGET_NAME}.cmake"
+      NAMESPACE ${PFL_PREFIX}::)
+
+    if(EXISTS
+       ${CMAKE_CURRENT_SOURCE_DIR}/misc/cmake/${TARGET_NAME}-config.cmake.in)
+      include(CMakePackageConfigHelpers)
+      # This will be used to replace @PACKAGE_cmakeModulesDir@
+      set(cmakeModulesDir cmake)
+
+      configure_package_config_file(
+        misc/cmake/${TARGET_NAME}-config.cmake.in
+        misc/cmake/${TARGET_NAME}-config.cmake
+        INSTALL_DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${TARGET_NAME}
+        PATH_VARS cmakeModulesDir
+        NO_SET_AND_CHECK_MACRO NO_CHECK_REQUIRED_COMPONENTS_MACRO)
+
+      write_basic_package_version_file(
+        ${CMAKE_CURRENT_BINARY_DIR}/misc/cmake/${TARGET_NAME}-config-version.cmake
+        VERSION ${PFL_ADD_LIBRARY_VERSION}
+        COMPATIBILITY SameMajorVersion)
+
+      install(
+        FILES
+          ${CMAKE_CURRENT_BINARY_DIR}/misc/cmake/${TARGET_NAME}-config.cmake
+          ${CMAKE_CURRENT_BINARY_DIR}/misc/cmake/${TARGET_NAME}-config-version.cmake
+        DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${TARGET_NAME})
+    endif()
+  endif()
+
+  if(PFL_PREFIX)
+    set(PFL_PREFIX "${PFL_PREFIX}::${TARGET_DIR_NAME}")
+  else()
+    set(PFL_PREFIX "${TARGET_DIR_NAME}")
+  endif()
+
+  if(PFL_ENABLE_TESTING AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/tests")
+    message(
+      STATUS
+        "PFL:${PFL_MESSAGE_INDENT} Adding tests for library ${TARGET_EXPORT_NAME} at ${CMAKE_CURRENT_SOURCE_DIR}/tests"
+    )
+    set(PFL_MESSAGE_INDENT "${PFL_MESSAGE_INDENT}  ")
+    add_subdirectory(tests)
+    string(SUBSTRING "${PFL_MESSAGE_INDENT}" 2 -1 PFL_MESSAGE_INDENT)
+  endif()
+
+  if(PFL_ADD_LIBRARY_EXAMPLES
+     AND PFL_BUILD_EXAMPLES
+     AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/examples")
+    message(
+      STATUS
+        "PFL:${PFL_MESSAGE_INDENT} Adding examples for library ${TARGET_EXPORT_NAME} at ${CMAKE_CURRENT_SOURCE_DIR}/examples"
+    )
+    set(PFL_MESSAGE_INDENT "${PFL_MESSAGE_INDENT}  ")
+    foreach(EXAMPLE ${PFL_ADD_LIBRARY_EXAMPLES})
+      add_subdirectory("examples/${EXAMPLE}")
+    endforeach()
+    string(SUBSTRING "${PFL_MESSAGE_INDENT}" 2 -1 PFL_MESSAGE_INDENT)
+  endif()
+
+  if(PFL_ADD_LIBRARY_APPS AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/apps")
+    message(
+      STATUS
+        "PFL:${PFL_MESSAGE_INDENT} Adding apps for library ${TARGET_EXPORT_NAME} at ${CMAKE_CURRENT_SOURCE_DIR}/apps"
+    )
+    set(PFL_MESSAGE_INDENT "${PFL_MESSAGE_INDENT}  ")
+    foreach(APP ${PFL_ADD_LIBRARY_APPS})
+      add_subdirectory("apps/${APP}")
+    endforeach()
+    string(SUBSTRING "${PFL_MESSAGE_INDENT}" 2 -1 PFL_MESSAGE_INDENT)
+  endif()
 endfunction()
 
+# This function is used to add executable, you should call this function if your
+# source under src/ is the source code of your executable file. For examples:
+# directories under apps, directories under examples or your project root if
+# your project is not a library but a application.
+#
+# LIBEXEC option: Whether your executable is a application should be used by
+# user directly or not. LIBEXEC executable will be installed to the LIBEXEC dir.
+#
+# INTERNAL option: Whether your executable is a internal executable. Internal
+# executable will not be install at all.
+#
+# OUTPUT_NAME string: The output file name of your executable.
+#
+# Other parameters is just like pfl_add_library.
 function(pfl_add_executable)
-        message (
-                STATUS
-                        "PFL: Building executable at"
-                        "${CMAKE_CURRENT_SOURCE_DIR} ..."
-        )
-
-        cmake_parse_arguments (
-                PFL_ADD_EXECUTABLE
-                "LIBEXEC;INTERNAL;NO_INSTALL"
-                "OUTPUT_NAME"
-                "INS;SOURCES;HEADERS;LINK_LIBRARIES;COMPILE_FEATURES"
-                ${ARGN}
-        )
-
-        cmake_path (
-                GET
-                CMAKE_CURRENT_SOURCE_DIR
-                FILENAME
-                TARGET_DIR_NAME
-        )
-
-        string (
-                REPLACE
-                        " " "_" TARGET_NAME "${TARGET_DIR_NAME}"
-        )
-
-        string (
-                REPLACE
-                        "::" "__" TARGET_PREFIX "${PFL_PREFIX}"
-        )
-
-        if(TARGET_PREFIX)
-                set (TARGET_NAME "${TARGET_PREFIX}__${TARGET_NAME}")
-        endif()
-
-        message (
-                STATUS
-                        "PFL: Adding executable ${TARGET_NAME} ..."
-        )
-
-        pfl_configure_files (
-                INS
-                ${PFL_ADD_EXECUTABLE_INS}
-                HEADERS
-                PFL_ADD_EXECUTABLE_HEADERS
-                SOURCES
-                PFL_ADD_EXECUTABLE_SOURCES
-        )
-
-        add_executable ("${TARGET_NAME}" ${PFL_ADD_EXECUTABLE_SOURCES})
-
-        if(PFL_ADD_EXECUTABLE_OUTPUT_NAME)
-                set_target_properties (
-                        "${TARGET_NAME}"
-                        PROPERTIES
-                                OUTPUT_NAME ${PFL_ADD_EXECUTABLE_OUTPUT_NAME}
-                )
-        endif()
-
-        target_sources (
-                ${TARGET_NAME}
-                PUBLIC
-                        FILE_SET HEADERS BASE_DIRS include
-                        ${CMAKE_CURRENT_BINARY_DIR}/include FILES
-                        ${PFL_ADD_EXECUTABLE_HEADERS}
-        )
-
-        target_include_directories (
-                ${TARGET_NAME} PRIVATE
-                                       src ${CMAKE_CURRENT_BINARY_DIR}/src
-        )
-
-        if(PFL_ADD_EXECUTABLE_LINK_LIBRARIES)
-                target_link_libraries (
-                        ${TARGET_NAME} ${PFL_ADD_EXECUTABLE_LINK_LIBRARIES}
-                )
-        endif()
-
-        if(PFL_ADD_EXECUTABLE_COMPILE_FEATURES)
-                target_compile_features (
-                        ${TARGET_NAME} ${PFL_ADD_EXECUTABLE_COMPILE_FEATURES}
-                )
-        endif()
-
-        if(PFL_ADD_EXECUTABLE_NO_INSTALL OR PFL_ADD_EXECUTABLE_INTERNAL)
-                return ()
-        endif()
-
-        if(PFL_ADD_EXECUTABLE_LIBEXEC)
-                include (GNUInstallDirs)
-
-                install (
-                        ${TARGET_NAME} DESTINATION
-                        ${CMAKE_INSTALL_LIBEXECDIR}/${TARGET_PREFIX}
-                )
-        endif()
+  cmake_parse_arguments(
+    PFL_ADD_EXECUTABLE "LIBEXEC;INTERNAL" "OUTPUT_NAME;INSTALL_PREFIX"
+    "INS;SOURCES;HEADERS;LINK_LIBRARIES;COMPILE_FEATURES" ${ARGN})
+
+  cmake_path(GET CMAKE_CURRENT_SOURCE_DIR FILENAME TARGET_DIR_NAME)
+
+  string(REPLACE " " "_" TARGET_NAME "${TARGET_DIR_NAME}")
+
+  string(REPLACE "::" "__" TARGET_PREFIX "${PFL_PREFIX}")
+
+  if(TARGET_PREFIX)
+    set(TARGET_NAME "${TARGET_PREFIX}__${TARGET_NAME}")
+  endif()
+
+  message(
+    STATUS
+      "PFL:${PFL_MESSAGE_INDENT} Adding executable ${TARGET_NAME} at ${CMAKE_CURRENT_SOURCE_DIR}"
+  )
+  set(PFL_MESSAGE_INDENT "${PFL_MESSAGE_INDENT}  ")
+
+  __pfl_configure_files(
+    INS ${PFL_ADD_EXECUTABLE_INS} HEADERS PFL_ADD_EXECUTABLE_HEADERS SOURCES
+    PFL_ADD_EXECUTABLE_SOURCES)
+
+  add_executable("${TARGET_NAME}" ${PFL_ADD_EXECUTABLE_SOURCES})
+
+  if(PFL_ADD_EXECUTABLE_OUTPUT_NAME)
+    set_target_properties(
+      "${TARGET_NAME}" PROPERTIES OUTPUT_NAME ${PFL_ADD_EXECUTABLE_OUTPUT_NAME})
+  endif()
+
+  target_sources(
+    ${TARGET_NAME}
+    PUBLIC FILE_SET
+           HEADERS
+           BASE_DIRS
+           include
+           ${CMAKE_CURRENT_BINARY_DIR}/include
+           FILES
+           ${PFL_ADD_EXECUTABLE_HEADERS})
+
+  target_include_directories(${TARGET_NAME}
+                             PRIVATE src ${CMAKE_CURRENT_BINARY_DIR}/src)
+
+  if(PFL_ADD_EXECUTABLE_LINK_LIBRARIES)
+    target_link_libraries(${TARGET_NAME} ${PFL_ADD_EXECUTABLE_LINK_LIBRARIES})
+  endif()
+
+  if(PFL_ADD_EXECUTABLE_COMPILE_FEATURES)
+    target_compile_features(${TARGET_NAME}
+                            ${PFL_ADD_EXECUTABLE_COMPILE_FEATURES})
+  endif()
+
+  if(PFL_ADD_EXECUTABLE_INTERNAL)
+    return()
+  endif()
+
+  include(GNUInstallDirs)
+
+  if(PFL_ADD_EXECUTABLE_LIBEXEC)
+    install(
+      TARGETS ${TARGET_NAME}
+      DESTINATION
+        ${CMAKE_INSTALL_LIBEXECDIR}/${PFL_ADD_EXECUTABLE_INSTALL_PREFIX})
+    return()
+  endif()
+
+  install(
+    TARGETS ${TARGET_NAME}
+    DESTINATION ${CMAKE_INSTALL_BINDIR}/${PFL_ADD_EXECUTABLE_INSTALL_PREFIX})
+
 endfunction()
diff --git a/libs/cli/CMakeLists.txt b/libs/cli/CMakeLists.txt
index df595a0..13b8530 100644
--- a/libs/cli/CMakeLists.txt
+++ b/libs/cli/CMakeLists.txt
@@ -1,5 +1,5 @@
 pfl_add_library(
-  NO_INSTALL # cli is not ready for publish
+  INTERNAL # cli is not ready for publish
   SOVERSION
   ${OCPPI_SOVERSION}
   VERSION
diff --git a/libs/cli/examples/using-crun/CMakeLists.txt b/libs/cli/examples/using-crun/CMakeLists.txt
index 23be15f..c214fc2 100644
--- a/libs/cli/examples/using-crun/CMakeLists.txt
+++ b/libs/cli/examples/using-crun/CMakeLists.txt
@@ -3,6 +3,7 @@ find_package(
 pkg_check_modules(SYSTEMD REQUIRED IMPORTED_TARGET systemd)
 
 pfl_add_executable(
+  INTERNAL
   SOURCES
   src/main.cpp
   LINK_LIBRARIES