diff --git a/contrib/10.math/math.c b/contrib/10.math/math.c
index cbaeec7a..187941ad 100644
--- a/contrib/10.math/math.c
+++ b/contrib/10.math/math.c
@@ -1,4 +1,5 @@
 #include "picrin.h"
+#include "picrin/extra.h"
 
 #include <math.h>
 
diff --git a/contrib/20.r7rs/src/file.c b/contrib/20.r7rs/src/file.c
index 5cb99ffc..62942ecd 100644
--- a/contrib/20.r7rs/src/file.c
+++ b/contrib/20.r7rs/src/file.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 
 #include <stdio.h>
 
diff --git a/contrib/20.r7rs/src/load.c b/contrib/20.r7rs/src/load.c
index b7459bb6..3503eda9 100644
--- a/contrib/20.r7rs/src/load.c
+++ b/contrib/20.r7rs/src/load.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 
 #include <stdio.h>
 
diff --git a/contrib/20.r7rs/src/mutable-string.c b/contrib/20.r7rs/src/mutable-string.c
index bc688e10..539d4680 100644
--- a/contrib/20.r7rs/src/mutable-string.c
+++ b/contrib/20.r7rs/src/mutable-string.c
@@ -1,4 +1,5 @@
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 
 void
diff --git a/contrib/20.r7rs/src/system.c b/contrib/20.r7rs/src/system.c
index fc5d2ecf..4d0fdb15 100644
--- a/contrib/20.r7rs/src/system.c
+++ b/contrib/20.r7rs/src/system.c
@@ -5,6 +5,7 @@
 #include <stdlib.h>
 
 #include "picrin.h"
+#include "picrin/extra.h"
 
 extern int picrin_argc;
 extern char **picrin_argv;
diff --git a/contrib/20.r7rs/src/time.c b/contrib/20.r7rs/src/time.c
index ac8585d3..5c325bbd 100644
--- a/contrib/20.r7rs/src/time.c
+++ b/contrib/20.r7rs/src/time.c
@@ -5,6 +5,7 @@
 #include <time.h>
 
 #include "picrin.h"
+#include "picrin/extra.h"
 
 #define UTC_TAI_DIFF 35
 
diff --git a/contrib/30.random/src/random.c b/contrib/30.random/src/random.c
index 95fb7a03..2c7f9d6f 100644
--- a/contrib/30.random/src/random.c
+++ b/contrib/30.random/src/random.c
@@ -1,4 +1,5 @@
 #include "picrin.h"
+#include "picrin/extra.h"
 
 double genrand_real3(void);
 
diff --git a/contrib/30.readline/src/readline.c b/contrib/30.readline/src/readline.c
index 1438b0a7..6153cdbb 100644
--- a/contrib/30.readline/src/readline.c
+++ b/contrib/30.readline/src/readline.c
@@ -6,6 +6,7 @@
 forget to use the C++ extern "C" to get it to compile.
 */
 #include "picrin.h"
+#include "picrin/extra.h"
 
 #include <editline/readline.h>
 
diff --git a/contrib/30.regexp/src/regexp.c b/contrib/30.regexp/src/regexp.c
index c77da4e8..8f7f0c89 100644
--- a/contrib/30.regexp/src/regexp.c
+++ b/contrib/30.regexp/src/regexp.c
@@ -1,4 +1,5 @@
 #include "picrin.h"
+#include "picrin/extra.h"
 
 #include <regex.h>
 
diff --git a/contrib/40.srfi/src/106.c b/contrib/40.srfi/src/106.c
index 3d1a0cdd..72633481 100644
--- a/contrib/40.srfi/src/106.c
+++ b/contrib/40.srfi/src/106.c
@@ -1,4 +1,5 @@
 #include "picrin.h"
+#include "picrin/extra.h"
 
 #include <errno.h>
 #include <netdb.h>
diff --git a/contrib/60.repl/repl.c b/contrib/60.repl/repl.c
index e6e371de..a4585e73 100644
--- a/contrib/60.repl/repl.c
+++ b/contrib/60.repl/repl.c
@@ -1,12 +1,11 @@
 #include "picrin.h"
+#include "picrin/extra.h"
 
 #include <unistd.h>
 
-
 static pic_value
 pic_repl_tty_p(pic_state *pic)
 {
-
   pic_get_args(pic, "");
 
   return pic_bool_value(pic, (isatty(STDIN_FILENO)));
diff --git a/etc/mkloader.pl b/etc/mkloader.pl
index 088bd962..be2d7414 100755
--- a/etc/mkloader.pl
+++ b/etc/mkloader.pl
@@ -12,6 +12,7 @@ print <<EOL;
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 
 EOL
 
diff --git a/extlib/benz/blob.c b/extlib/benz/blob.c
index db0d6079..f1367b04 100644
--- a/extlib/benz/blob.c
+++ b/extlib/benz/blob.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 
 pic_value
diff --git a/extlib/benz/debug.c b/extlib/benz/debug.c
index bc96a209..db0ef8b2 100644
--- a/extlib/benz/debug.c
+++ b/extlib/benz/debug.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 #include "picrin/state.h"
 
diff --git a/extlib/benz/dict.c b/extlib/benz/dict.c
index 8675d5e9..b8510034 100644
--- a/extlib/benz/dict.c
+++ b/extlib/benz/dict.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 
 KHASH_DEFINE(dict, pic_sym *, pic_value, kh_ptr_hash_func, kh_ptr_hash_equal)
diff --git a/extlib/benz/error.c b/extlib/benz/error.c
index b750a19a..541744ea 100644
--- a/extlib/benz/error.c
+++ b/extlib/benz/error.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 #include "picrin/state.h"
 
diff --git a/extlib/benz/eval.c b/extlib/benz/eval.c
index 02393339..0b7976c2 100644
--- a/extlib/benz/eval.c
+++ b/extlib/benz/eval.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 #include "picrin/opcode.h"
 #include "picrin/state.h"
diff --git a/extlib/benz/include/picrin.h b/extlib/benz/include/picrin.h
index 0bfd26e2..330421b0 100644
--- a/extlib/benz/include/picrin.h
+++ b/extlib/benz/include/picrin.h
@@ -291,121 +291,6 @@ int xfprintf(pic_state *, xFILE *fp, const char *fmt, ...);
 int xvfprintf(pic_state *, xFILE *fp, const char *fmt, va_list);
 
 
-
-/* extra stuff */
-
-
-void *pic_default_allocf(void *, void *, size_t);
-
-#define pic_assert_type(pic, v, type)                           \
-  if (! pic_##type##_p(pic, v)) {                               \
-    pic_errorf(pic, "expected " #type ", but got ~s", v);       \
-  }
-
-xFILE *xfile_xstdin(pic_state *);
-xFILE *xfile_xstdout(pic_state *);
-xFILE *xfile_xstderr(pic_state *);
-
-#define xstdin  (xfile_xstdin(pic))
-#define xstdout (xfile_xstdout(pic))
-#define xstderr (xfile_xstderr(pic))
-
-#if PIC_ENABLE_STDIO
-xFILE *xfopen_file(pic_state *, FILE *, const char *mode);
-#endif
-xFILE *xfopen_buf(pic_state *, const char *buf, int len, const char *mode);
-int xfget_buf(pic_state *, xFILE *file, const char **buf, int *len);
-xFILE *xfopen_null(pic_state *, const char *mode);
-
-#define pic_void(exec)                          \
-  pic_void_(PIC_GENSYM(ai), exec)
-#define pic_void_(ai,exec) do {                 \
-    size_t ai = pic_enter(pic);                 \
-    exec;                                       \
-    pic_leave(pic, ai);                         \
-  } while (0)
-
-pic_value pic_read(pic_state *, pic_value port);
-pic_value pic_read_cstr(pic_state *, const char *);
-
-pic_value pic_expand(pic_state *, pic_value program, pic_value env);
-
-pic_value pic_eval(pic_state *, pic_value program, const char *lib);
-
-void pic_load(pic_state *, pic_value port);
-void pic_load_cstr(pic_state *, const char *);
-
-#define pic_deflibrary(pic, lib) do {           \
-    if (! pic_find_library(pic, lib)) {         \
-      pic_make_library(pic, lib);               \
-    }                                           \
-    pic_in_library(pic, lib);                   \
-  } while (0)
-
-struct pic_cont *pic_alloca_cont(pic_state *);
-pic_value pic_make_cont(pic_state *, struct pic_cont *);
-void pic_push_native_handler(pic_state *, struct pic_cont *);
-void pic_push_handler(pic_state *, pic_value);
-pic_value pic_pop_handler(pic_state *);
-void pic_save_point(pic_state *, struct pic_cont *, PIC_JMPBUF *);
-void pic_exit_point(pic_state *);
-
-/* do not return from try block! */
-
-pic_value pic_err(pic_state *);
-
-#define pic_try                                 \
-  pic_try_(PIC_GENSYM(cont), PIC_GENSYM(handler))
-#define pic_catch                               \
-  pic_catch_(PIC_GENSYM(label))
-#define pic_try_(cont, handler)                                         \
-  do {                                                                  \
-    PIC_JMPBUF jmp;                                                     \
-    struct pic_cont *cont = pic_alloca_cont(pic);                       \
-    if (PIC_SETJMP(pic, jmp) == 0) {                                    \
-      pic_save_point(pic, cont, &jmp);                                  \
-      pic_push_native_handler(pic, cont);
-#define pic_catch_(label)                                 \
-      pic_pop_handler(pic);                               \
-      pic_exit_point(pic);                                \
-    } else {                                              \
-      goto label;                                         \
-    }                                                     \
-  } while (0);                                            \
-  if (0)                                                  \
-  label:
-
-PIC_NORETURN void pic_error(pic_state *, const char *type, const char *msg, pic_value irrs);
-
-#define pic_for_each(var, list, it)                                     \
-  for (it = (list); ! pic_nil_p(pic, it); it = pic_cdr(pic, it))        \
-    if ((var = pic_car(pic, it)), true)
-
-#define pic_push(pic, item, place) (place = pic_cons(pic, item, place))
-#define pic_pop(pic, place) (place = pic_cdr(pic, place))
-
-void pic_warnf(pic_state *, const char *, ...);
-pic_value pic_get_backtrace(pic_state *);
-void pic_print_backtrace(pic_state *, xFILE *);
-
-#define pic_stdin(pic) pic_funcall(pic, "picrin.base", "current-input-port", 0)
-#define pic_stdout(pic) pic_funcall(pic, "picrin.base", "current-output-port", 0)
-#define pic_stderr(pic) pic_funcall(pic, "picrin.base", "current-error-port", 0)
-
-pic_value pic_write(pic_state *, pic_value); /* returns given obj */
-pic_value pic_fwrite(pic_state *, pic_value, xFILE *);
-void pic_printf(pic_state *, const char *, ...);
-void pic_fprintf(pic_state *, pic_value port, const char *, ...);
-pic_value pic_display(pic_state *, pic_value);
-pic_value pic_fdisplay(pic_state *, pic_value, xFILE *);
-
-pic_value pic_library_environment(pic_state *, const char *);
-
-#if DEBUG
-# define pic_debug(pic,obj) pic_fwrite(pic,obj,xstderr)
-# define pic_fdebug(pic,obj,file) pic_fwrite(pic,obj,file)
-#endif
-
 #if defined(__cplusplus)
 }
 #endif
diff --git a/extlib/benz/include/picrin/extra.h b/extlib/benz/include/picrin/extra.h
new file mode 100644
index 00000000..6cddf97d
--- /dev/null
+++ b/extlib/benz/include/picrin/extra.h
@@ -0,0 +1,131 @@
+/**
+ * See Copyright Notice in picrin.h
+ */
+
+#ifndef PICRIN_EXTRA_H
+#define PICRIN_EXTRA_H
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+
+#if PIC_ENABLE_LIBC
+void *pic_default_allocf(void *, void *, size_t);
+#endif
+
+
+#define pic_assert_type(pic, v, type)                           \
+  if (! pic_##type##_p(pic, v)) {                               \
+    pic_errorf(pic, "expected " #type ", but got ~s", v);       \
+  }
+
+xFILE *xfile_xstdin(pic_state *);
+xFILE *xfile_xstdout(pic_state *);
+xFILE *xfile_xstderr(pic_state *);
+
+#define xstdin  (xfile_xstdin(pic))
+#define xstdout (xfile_xstdout(pic))
+#define xstderr (xfile_xstderr(pic))
+
+#if PIC_ENABLE_STDIO
+xFILE *xfopen_file(pic_state *, FILE *, const char *mode);
+#endif
+xFILE *xfopen_buf(pic_state *, const char *buf, int len, const char *mode);
+int xfget_buf(pic_state *, xFILE *file, const char **buf, int *len);
+xFILE *xfopen_null(pic_state *, const char *mode);
+
+#define pic_void(exec)                          \
+  pic_void_(PIC_GENSYM(ai), exec)
+#define pic_void_(ai,exec) do {                 \
+    size_t ai = pic_enter(pic);                 \
+    exec;                                       \
+    pic_leave(pic, ai);                         \
+  } while (0)
+
+pic_value pic_read(pic_state *, pic_value port);
+pic_value pic_read_cstr(pic_state *, const char *);
+
+pic_value pic_expand(pic_state *, pic_value program, pic_value env);
+
+pic_value pic_eval(pic_state *, pic_value program, const char *lib);
+
+void pic_load(pic_state *, pic_value port);
+void pic_load_cstr(pic_state *, const char *);
+
+#define pic_deflibrary(pic, lib) do {           \
+    if (! pic_find_library(pic, lib)) {         \
+      pic_make_library(pic, lib);               \
+    }                                           \
+    pic_in_library(pic, lib);                   \
+  } while (0)
+
+struct pic_cont *pic_alloca_cont(pic_state *);
+pic_value pic_make_cont(pic_state *, struct pic_cont *);
+void pic_push_native_handler(pic_state *, struct pic_cont *);
+void pic_push_handler(pic_state *, pic_value);
+pic_value pic_pop_handler(pic_state *);
+void pic_save_point(pic_state *, struct pic_cont *, PIC_JMPBUF *);
+void pic_exit_point(pic_state *);
+
+/* do not return from try block! */
+
+pic_value pic_err(pic_state *);
+
+#define pic_try                                 \
+  pic_try_(PIC_GENSYM(cont), PIC_GENSYM(handler))
+#define pic_catch                               \
+  pic_catch_(PIC_GENSYM(label))
+#define pic_try_(cont, handler)                                         \
+  do {                                                                  \
+    PIC_JMPBUF jmp;                                                     \
+    struct pic_cont *cont = pic_alloca_cont(pic);                       \
+    if (PIC_SETJMP(pic, jmp) == 0) {                                    \
+      pic_save_point(pic, cont, &jmp);                                  \
+      pic_push_native_handler(pic, cont);
+#define pic_catch_(label)                                 \
+      pic_pop_handler(pic);                               \
+      pic_exit_point(pic);                                \
+    } else {                                              \
+      goto label;                                         \
+    }                                                     \
+  } while (0);                                            \
+  if (0)                                                  \
+  label:
+
+PIC_NORETURN void pic_error(pic_state *, const char *type, const char *msg, pic_value irrs);
+
+#define pic_for_each(var, list, it)                                     \
+  for (it = (list); ! pic_nil_p(pic, it); it = pic_cdr(pic, it))        \
+    if ((var = pic_car(pic, it)), true)
+
+#define pic_push(pic, item, place) (place = pic_cons(pic, item, place))
+#define pic_pop(pic, place) (place = pic_cdr(pic, place))
+
+void pic_warnf(pic_state *, const char *, ...);
+pic_value pic_get_backtrace(pic_state *);
+void pic_print_backtrace(pic_state *, xFILE *);
+
+#define pic_stdin(pic) pic_funcall(pic, "picrin.base", "current-input-port", 0)
+#define pic_stdout(pic) pic_funcall(pic, "picrin.base", "current-output-port", 0)
+#define pic_stderr(pic) pic_funcall(pic, "picrin.base", "current-error-port", 0)
+
+pic_value pic_write(pic_state *, pic_value); /* returns given obj */
+pic_value pic_fwrite(pic_state *, pic_value, xFILE *);
+void pic_printf(pic_state *, const char *, ...);
+void pic_fprintf(pic_state *, pic_value port, const char *, ...);
+pic_value pic_display(pic_state *, pic_value);
+pic_value pic_fdisplay(pic_state *, pic_value, xFILE *);
+
+pic_value pic_library_environment(pic_state *, const char *);
+
+#if DEBUG
+# define pic_debug(pic,obj) pic_fwrite(pic,obj,xstderr)
+# define pic_fdebug(pic,obj,file) pic_fwrite(pic,obj,file)
+#endif
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif
diff --git a/extlib/benz/lib.c b/extlib/benz/lib.c
index 63ea7a93..7bcfbe50 100644
--- a/extlib/benz/lib.c
+++ b/extlib/benz/lib.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 #include "picrin/state.h"
 
diff --git a/extlib/benz/load.c b/extlib/benz/load.c
index 7272c000..25d79d7d 100644
--- a/extlib/benz/load.c
+++ b/extlib/benz/load.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 
 void
 pic_load(pic_state *pic, pic_value port)
diff --git a/extlib/benz/macro.c b/extlib/benz/macro.c
index 2f8dc9cd..58f87f98 100644
--- a/extlib/benz/macro.c
+++ b/extlib/benz/macro.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 #include "picrin/state.h"
 
diff --git a/extlib/benz/number.c b/extlib/benz/number.c
index 08a2a2a8..2c6d8d37 100644
--- a/extlib/benz/number.c
+++ b/extlib/benz/number.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 
 static pic_value
 pic_number_number_p(pic_state *pic)
diff --git a/extlib/benz/pair.c b/extlib/benz/pair.c
index ec95a029..9a418489 100644
--- a/extlib/benz/pair.c
+++ b/extlib/benz/pair.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 
 pic_value
diff --git a/extlib/benz/port.c b/extlib/benz/port.c
index af8a1f5b..3b4decb6 100644
--- a/extlib/benz/port.c
+++ b/extlib/benz/port.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 #include "picrin/file.h"
 
diff --git a/extlib/benz/proc.c b/extlib/benz/proc.c
index 5182a6b5..9b6e0010 100644
--- a/extlib/benz/proc.c
+++ b/extlib/benz/proc.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 #include "picrin/opcode.h"
 #include "picrin/state.h"
diff --git a/extlib/benz/read.c b/extlib/benz/read.c
index 39404653..baa13123 100644
--- a/extlib/benz/read.c
+++ b/extlib/benz/read.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 #include "picrin/state.h"
 
diff --git a/extlib/benz/state.c b/extlib/benz/state.c
index afd0c412..9557963a 100644
--- a/extlib/benz/state.c
+++ b/extlib/benz/state.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 #include "picrin/state.h"
 
diff --git a/extlib/benz/string.c b/extlib/benz/string.c
index ea84ae4b..7f834138 100644
--- a/extlib/benz/string.c
+++ b/extlib/benz/string.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 
 struct pic_chunk {
diff --git a/extlib/benz/symbol.c b/extlib/benz/symbol.c
index b073421e..0fa0ab63 100644
--- a/extlib/benz/symbol.c
+++ b/extlib/benz/symbol.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 #include "picrin/state.h"
 
diff --git a/extlib/benz/var.c b/extlib/benz/var.c
index df5ee003..4eb048e0 100644
--- a/extlib/benz/var.c
+++ b/extlib/benz/var.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 #include "picrin/state.h"
 
diff --git a/extlib/benz/vector.c b/extlib/benz/vector.c
index 7ae1d824..402f36c8 100644
--- a/extlib/benz/vector.c
+++ b/extlib/benz/vector.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 
 pic_value
diff --git a/extlib/benz/write.c b/extlib/benz/write.c
index d9822db3..c3b68ba5 100644
--- a/extlib/benz/write.c
+++ b/extlib/benz/write.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 #include "picrin/object.h"
 #include "picrin/state.h"
 
diff --git a/src/main.c b/src/main.c
index 35d627dd..4878812f 100644
--- a/src/main.c
+++ b/src/main.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 
 void
 pic_init_picrin(pic_state *pic)