diff --git a/cmake/FindFLEX.cmake b/cmake/FindFLEX.cmake
deleted file mode 100644
index c56e8eda..00000000
--- a/cmake/FindFLEX.cmake
+++ /dev/null
@@ -1,179 +0,0 @@
-# - Find flex executable and provides a macro to generate custom build rules
-#
-# The module defines the following variables:
-#  FLEX_FOUND - true is flex executable is found
-#  FLEX_EXECUTABLE - the path to the flex executable
-#  FLEX_VERSION - the version of flex
-#  FLEX_LIBRARIES - The flex libraries
-#
-# The minimum required version of flex can be specified using the
-# standard syntax, e.g. FIND_PACKAGE(FLEX 2.5.13)
-#
-#
-# If flex is found on the system, the module provides the macro:
-#  FLEX_TARGET(Name FlexInput FlexOutput [COMPILE_FLAGS <string>])
-# which creates a custom command  to generate the <FlexOutput> file from
-# the <FlexInput> file.  If  COMPILE_FLAGS option is specified, the next
-# parameter is added to the flex  command line. Name is an alias used to
-# get  details of  this custom  command.  Indeed the  macro defines  the
-# following variables:
-#  FLEX_${Name}_DEFINED - true is the macro ran successfully
-#  FLEX_${Name}_OUTPUTS - the source file generated by the custom rule, an
-#  alias for FlexOutput
-#  FLEX_${Name}_INPUT - the flex source file, an alias for ${FlexInput}
-#
-# Flex scanners oftenly use tokens  defined by Bison: the code generated
-# by Flex  depends of the header  generated by Bison.   This module also
-# defines a macro:
-#  ADD_FLEX_BISON_DEPENDENCY(FlexTarget BisonTarget)
-# which  adds the  required dependency  between a  scanner and  a parser
-# where  <FlexTarget>  and <BisonTarget>  are  the  first parameters  of
-# respectively FLEX_TARGET and BISON_TARGET macros.
-#
-#  ====================================================================
-#  Example:
-#
-#   find_package(BISON)
-#   find_package(FLEX)
-#
-#   BISON_TARGET(MyParser parser.y ${CMAKE_CURRENT_BINARY_DIR}/parser.cpp
-#   FLEX_TARGET(MyScanner lexer.l  ${CMAKE_CURRENT_BIANRY_DIR}/lexer.cpp)
-#   ADD_FLEX_BISON_DEPENDENCY(MyScanner MyParser)
-#
-#   include_directories(${CMAKE_CURRENT_BINARY_DIR})
-#   add_executable(Foo
-#      Foo.cc
-#      ${BISON_MyParser_OUTPUTS}
-#      ${FLEX_MyScanner_OUTPUTS}
-#   )
-#  ====================================================================
-
-#=============================================================================
-# Copyright 2009 Kitware, Inc.
-# Copyright 2006 Tristan Carel
-# Modified 2010 by Jon Siwek, backporting for CMake 2.6 compat
-#
-# Distributed under the OSI-approved BSD License (the "License"):
-# CMake - Cross Platform Makefile Generator
-# Copyright 2000-2009 Kitware, Inc., Insight Software Consortium
-# All rights reserved.
-
-# Redistribution and use in source and binary forms, with or without
-# modification, are permitted provided that the following conditions
-# are met:
-#
-# * Redistributions of source code must retain the above copyright
-#   notice, this list of conditions and the following disclaimer.
-#
-# * Redistributions in binary form must reproduce the above copyright
-#   notice, this list of conditions and the following disclaimer in the
-#   documentation and/or other materials provided with the distribution.
-#
-# * Neither the names of Kitware, Inc., the Insight Software Consortium,
-#   nor the names of their contributors may be used to endorse or promote
-#   products derived from this software without specific prior written
-#   permission.
-#
-# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-# HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-#
-# This software is distributed WITHOUT ANY WARRANTY; without even the
-# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
-# See the License for more information.
-#=============================================================================
-
-FIND_PROGRAM(FLEX_EXECUTABLE flex DOC "path to the flex executable")
-MARK_AS_ADVANCED(FLEX_EXECUTABLE)
-
-FIND_LIBRARY(FL_LIBRARY NAMES fl
-  DOC "path to the fl library")
-MARK_AS_ADVANCED(FL_LIBRARY)
-SET(FLEX_LIBRARIES ${FL_LIBRARY})
-
-IF(FLEX_EXECUTABLE)
-
-  EXECUTE_PROCESS(COMMAND ${FLEX_EXECUTABLE} --version
-    OUTPUT_VARIABLE FLEX_version_output
-    ERROR_VARIABLE FLEX_version_error
-    RESULT_VARIABLE FLEX_version_result
-    OUTPUT_STRIP_TRAILING_WHITESPACE)
-  IF(NOT ${FLEX_version_result} EQUAL 0)
-    IF(FLEX_FIND_REQUIRED)
-      MESSAGE(SEND_ERROR "Command \"${FLEX_EXECUTABLE} --version\" failed with output:\n${FLEX_version_output}\n${FLEX_version_error}")
-    ELSE()
-      MESSAGE("Command \"${FLEX_EXECUTABLE} --version\" failed with output:\n${FLEX_version_output}\n${FLEX_version_error}\nFLEX_VERSION will not be available")
-    ENDIF()
-  ELSE()
-    STRING(REGEX REPLACE "^flex (.*)$" "\\1"
-      FLEX_VERSION "${FLEX_version_output}")
-  ENDIF()
-
-  #============================================================
-  # FLEX_TARGET (public macro)
-  #============================================================
-  #
-  MACRO(FLEX_TARGET Name Input Output)
-    SET(FLEX_TARGET_usage "FLEX_TARGET(<Name> <Input> <Output> [COMPILE_FLAGS <string>]")
-    IF(${ARGC} GREATER 3)
-      IF(${ARGC} EQUAL 5)
-        IF("${ARGV3}" STREQUAL "COMPILE_FLAGS")
-          SET(FLEX_EXECUTABLE_opts  "${ARGV4}")
-          SEPARATE_ARGUMENTS(FLEX_EXECUTABLE_opts)
-        ELSE()
-          MESSAGE(SEND_ERROR ${FLEX_TARGET_usage})
-        ENDIF()
-      ELSE()
-        MESSAGE(SEND_ERROR ${FLEX_TARGET_usage})
-      ENDIF()
-    ENDIF()
-
-    ADD_CUSTOM_COMMAND(OUTPUT ${Output}
-      COMMAND ${FLEX_EXECUTABLE}
-      ARGS ${FLEX_EXECUTABLE_opts} -o${Output} ${Input}
-      DEPENDS ${Input}
-      COMMENT "[FLEX][${Name}] Building scanner with flex ${FLEX_VERSION}"
-      WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
-
-    SET(FLEX_${Name}_DEFINED TRUE)
-    SET(FLEX_${Name}_OUTPUTS ${Output})
-    SET(FLEX_${Name}_INPUT ${Input})
-    SET(FLEX_${Name}_COMPILE_FLAGS ${FLEX_EXECUTABLE_opts})
-  ENDMACRO(FLEX_TARGET)
-  #============================================================
-
-
-  #============================================================
-  # ADD_FLEX_BISON_DEPENDENCY (public macro)
-  #============================================================
-  #
-  MACRO(ADD_FLEX_BISON_DEPENDENCY FlexTarget BisonTarget)
-
-    IF(NOT FLEX_${FlexTarget}_OUTPUTS)
-      MESSAGE(SEND_ERROR "Flex target `${FlexTarget}' does not exists.")
-    ENDIF()
-
-    IF(NOT BISON_${BisonTarget}_OUTPUT_HEADER)
-      MESSAGE(SEND_ERROR "Bison target `${BisonTarget}' does not exists.")
-    ENDIF()
-
-    SET_SOURCE_FILES_PROPERTIES(${FLEX_${FlexTarget}_OUTPUTS}
-      PROPERTIES OBJECT_DEPENDS ${BISON_${BisonTarget}_OUTPUT_HEADER})
-  ENDMACRO(ADD_FLEX_BISON_DEPENDENCY)
-  #============================================================
-
-ENDIF(FLEX_EXECUTABLE)
-
-INCLUDE(FindPackageHandleStandardArgs)
-FIND_PACKAGE_HANDLE_STANDARD_ARGS(FLEX FLEX_EXECUTABLE
-                                       FLEX_VERSION)
-
-# FindFLEX.cmake ends here
diff --git a/include/picrin/parse.h b/include/picrin/parse.h
deleted file mode 100644
index 0451d201..00000000
--- a/include/picrin/parse.h
+++ /dev/null
@@ -1,46 +0,0 @@
-/**
- * See Copyright Notice in picrin.h
- */
-
-#ifndef PICRIN_PARSE_H__
-#define PICRIN_PARSE_H__
-
-#if defined(__cplusplus)
-extern "C" {
-#endif
-
-enum {
-  tEOF = 0,
-  tLABEL_SET, tLABEL_REF, tDATUM_COMMENT,
-  tLPAREN, tRPAREN, tLBRACKET, tRBRACKET, tDOT, tVPAREN,
-  tQUOTE, tQUASIQUOTE, tUNQUOTE, tUNQUOTE_SPLICING,
-  tINT, tBOOLEAN,
-  tFLOAT,
-  tSYMBOL, tSTRING,
-  tCHAR,
-  tBYTEVECTOR,
-};
-
-typedef union YYSTYPE {
-  int i;
-  double f;
-  struct {
-    char *dat;
-    size_t len;
-  } buf;
-  char c;
-} YYSTYPE;
-
-struct parser_control {
-  pic_state *pic;
-  YYSTYPE yylval;
-  xhash labels;
-  jmp_buf jmp;
-  const char *msg;
-};
-
-#if defined(__cplusplus)
-}
-#endif
-
-#endif
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 7a727e9b..9318f442 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,8 +1,3 @@
-# flex
-find_package(FLEX REQUIRED)
-flex_target(scan src/scan.l ${PROJECT_SOURCE_DIR}/src/lex.yy.c COMPILE_FLAGS --header-file="src/lex.yy.h")
-set_directory_properties(PROPERTIES ADDITIONAL_MAKE_CLEAN_FILES ${PROJECT_SOURCE_DIR}/src/lex.yy.h)
-
 # xfile
 set(XFILE_SOURCES extlib/xfile/xfile.c)
 
@@ -18,7 +13,7 @@ add_custom_command(
 
 # build!
 file(GLOB PICRIN_SOURCES ${PROJECT_SOURCE_DIR}/src/*.c)
-add_library(picrin SHARED ${PICRIN_SOURCES} ${PICLIB_SOURCE} ${FLEX_scan_OUTPUTS} ${XFILE_SOURCES} ${PICRIN_CONTRIB_SOURCES})
+add_library(picrin SHARED ${PICRIN_SOURCES} ${PICLIB_SOURCE} ${XFILE_SOURCES} ${PICRIN_CONTRIB_SOURCES})
 target_link_libraries(picrin m ${PICRIN_CONTRIB_LIBRARIES})
 
 # install
diff --git a/src/scan.l b/src/scan.l
deleted file mode 100644
index 747f31a7..00000000
--- a/src/scan.l
+++ /dev/null
@@ -1,230 +0,0 @@
-/**
- * See Copyright Notice in picrin.h
- */
-
-%{
-#include "picrin.h"
-#include "picrin/parse.h"
-
-#define yylval (yyextra->yylval)
-
-#define YY_NO_UNISTD_H
-
-/* NOTE:
- *  An internal function `yy_fatal_error` takes yyscanner for its second
- * argument but doesn't use it. This invokes a `unused variable` compiler
- * warning and it became super unusable if `-Werror` is turned on the system.
- * Since there's no flag to switch `yy_fatal_error` off and replace it with
- * a user-defined function, we modify this macro constant to use yyscanner
- * at least once avoiding get flex affected in any condition.
- */
-#define YY_EXIT_FAILURE ( (void)yyscanner, 2 )
-%}
-
-%option reentrant
-
-%option noyyalloc
-%option noyyrealloc
-%option noyyfree
-%option noinput
-%option nounput
-%option noyywrap
-
-%option extra-type="struct parser_control *"
-%option never-interactive
-
-  /* shebang */
-shebang		#!.*$
-
-  /* comment */
-comment		;.*$
-
-  /* boolean */
-boolean		#t|#f|#true|#false
-
-  /* symbol */
-identifier	[a-z0-9A-Z+/*!$%&:@^~?<=>_.-]+
-
-  /* number */
-digit		[0-9]
-real		{sign}{ureal}|{infnan}
-ureal		{uinteger}|\.{digit}+|{digit}+\.{digit}*
-integer		{sign}{uinteger}
-uinteger	{digit}+
-sign		[+-]?
-infnan		"+inf.0"|"-inf.0"|"+nan.0"|"-nan.0"
-
-  /* char */
-%x CHAR
-
-  /* string */
-%x STRING
-
-  /* bytevector */
-%x BYTEVECTOR
-
-  /* block comment */
-%x BLOCK_COMMENT
-
-  /* datum label */
-label		#{uinteger}
-%x DATUM_LABEL
-
-%%
-
-[ \t\n\r]	/* skip whitespace */
-{comment}	/* skip comment */
-{shebang}	/* skip shebang */
-
-"#|"		{
-  BEGIN(BLOCK_COMMENT);
-  yylval.i = 0;
-}
-<BLOCK_COMMENT>"#|" 	{
-  yylval.i++;
-}
-<BLOCK_COMMENT>"|#"	{
-  if (yylval.i == 0)
-    BEGIN(INITIAL);
-  else
-    yylval.i--;
-}
-<BLOCK_COMMENT>.|\n	{
-  /* skip block comment */
-}
-
-{label}		{
-  BEGIN(DATUM_LABEL);
-  yylval.i = atoi(yytext + 1);
-}
-<DATUM_LABEL>=	{
-  BEGIN(INITIAL);
-  return tLABEL_SET;
-}
-<DATUM_LABEL>#	{
-  BEGIN(INITIAL);
-  return tLABEL_REF;
-}
-
-"#;"		return tDATUM_COMMENT;
-"."		return tDOT;
-"("		return tLPAREN;
-")"		return tRPAREN;
-"["		return tLBRACKET;
-"]"		return tRBRACKET;
-"#("		return tVPAREN;
-"'"		return tQUOTE;
-"`"		return tQUASIQUOTE;
-","		return tUNQUOTE;
-",@"		return tUNQUOTE_SPLICING;
-
-{boolean}	{
-  yylval.i = (yytext[1] == 't');
-  return tBOOLEAN;
-}
-
-{integer}	{
-  yylval.i = atoi(yytext);
-  return tINT;
-}
-
-{real} 		{
-  yylval.f = atof(yytext);
-  return tFLOAT;
-}
-
-{identifier}	{
-  yylval.buf.dat = yytext;
-  yylval.buf.len = yyleng;
-  return tSYMBOL;
-}
-
-"\""		{
-  BEGIN(STRING);
-  yylval.buf.len = 0;
-  yylval.buf.dat = yyalloc(yylval.buf.len + 1, yyscanner);
-  strcpy(yylval.buf.dat, "");
-}
-<STRING>[^\\"]+	{
-  yylval.buf.len += yyleng;
-  yylval.buf.dat = yyrealloc(yylval.buf.dat, yylval.buf.len + 1, yyscanner);
-  strcpy(yylval.buf.dat + yylval.buf.len - yyleng, yytext);
-}
-<STRING>\\.	{
-  yylval.buf.len += 1;
-  yylval.buf.dat = yyrealloc(yylval.buf.dat, yylval.buf.len + 1, yyscanner);
-  yylval.buf.dat[yylval.buf.len] = '\0';
-
-  switch (yytext[yyleng - 1]) {
-  case 'a': yylval.buf.dat[yylval.buf.len - 1] = '\a'; break;
-  case 'b': yylval.buf.dat[yylval.buf.len - 1] = '\b'; break;
-  case 't': yylval.buf.dat[yylval.buf.len - 1] = '\t'; break;
-  case 'n': yylval.buf.dat[yylval.buf.len - 1] = '\n'; break;
-  case 'r': yylval.buf.dat[yylval.buf.len - 1] = '\r'; break;
-  default: yylval.buf.dat[yylval.buf.len - 1] = yytext[yyleng - 1]; break;
-  }
-}
-<STRING>\\[:blank:]*\n[:blank:]* {
-  /* skip intraline whitespaces */
-}
-<STRING>\"	{
-  BEGIN(INITIAL);
-  return tSTRING;
-}
-
-#\\		{
-  BEGIN(CHAR);
-}
-<CHAR>alarm	{ yylval.c = '\a'; BEGIN(INITIAL); return tCHAR; }
-<CHAR>backspace	{ yylval.c = '\b'; BEGIN(INITIAL); return tCHAR; }
-<CHAR>delete	{ yylval.c = 0x7f; BEGIN(INITIAL); return tCHAR; }
-<CHAR>escape	{ yylval.c = 0x1b; BEGIN(INITIAL); return tCHAR; }
-<CHAR>newline	{ yylval.c = '\n'; BEGIN(INITIAL); return tCHAR; }
-<CHAR>null	{ yylval.c = '\0'; BEGIN(INITIAL); return tCHAR; }
-<CHAR>return	{ yylval.c = '\r'; BEGIN(INITIAL); return tCHAR; }
-<CHAR>space	{ yylval.c = ' ';  BEGIN(INITIAL); return tCHAR; }
-<CHAR>tab	{ yylval.c = '\t'; BEGIN(INITIAL); return tCHAR; }
-<CHAR>.		{ yylval.c = yytext[0]; BEGIN(INITIAL); return tCHAR; }
-
-"#u8("		{
-  BEGIN(BYTEVECTOR);
-  yylval.buf.len = 0;
-  yylval.buf.dat = NULL;
-}
-<BYTEVECTOR>[ \r\n\t]	{
-  /* skip whitespace */
-}
-<BYTEVECTOR>{uinteger}	{
-  int i = atoi(yytext);
-  if (0 > i || i > 255) {
-    yyfree(yylval.buf.dat, yyscanner);
-    REJECT;
-  }
-  yylval.buf.len += 1;
-  yylval.buf.dat = yyrealloc(yylval.buf.dat, yylval.buf.len, yyscanner);
-  yylval.buf.dat[yylval.buf.len - 1] = (char)i;
-}
-<BYTEVECTOR>")"	{
-  BEGIN(INITIAL);
-  return tBYTEVECTOR;
-}
-
-%%
-
-void *
-yyalloc(size_t bytes, yyscan_t yyscanner)
-{
-  return pic_alloc(yyget_extra(yyscanner)->pic, bytes);
-}
-
-void *
-yyrealloc(void *ptr, size_t bytes, yyscan_t yyscanner)
-{
-  return pic_realloc(yyget_extra(yyscanner)->pic, ptr, bytes);
-}
-
-void
-yyfree(void * ptr, yyscan_t yyscanner)
-{
-  return pic_free(yyget_extra(yyscanner)->pic, ptr);
-}