diff --git a/lib/Makefile b/lib/Makefile
index 96346307..6ea0b819 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -2,7 +2,6 @@ LIBPICRIN_SRCS = \
 	blob.c\
 	bool.c\
 	char.c\
-	cont.c\
 	data.c\
 	dict.c\
 	error.c\
@@ -19,6 +18,7 @@ LIBPICRIN_SRCS = \
 	var.c\
 	vector.c\
 	weak.c\
+	ext/cont.c\
 	ext/eval.c\
 	ext/read.c\
 	ext/write.c\
@@ -36,7 +36,7 @@ LIBPICRIN_HEADERS = \
 	object.h\
 	state.h
 
-CFLAGS += -I./include -Wall -Wextra -g
+override CFLAGS += -I./include -Wall -Wextra -g
 
 mini-picrin: ext/main.o libpicrin.a
 	$(CC) $(CFLAGS) -o $@ ext/main.o libpicrin.a
diff --git a/lib/cont.c b/lib/cont.c
deleted file mode 100644
index 96ae47ea..00000000
--- a/lib/cont.c
+++ /dev/null
@@ -1,183 +0,0 @@
-/**
- * See Copyright Notice in picrin.h
- */
-
-#include "picrin.h"
-#include "object.h"
-#include "state.h"
-
-#if PIC_USE_CALLCC
-
-static pic_value
-cont_call(pic_state *pic)
-{
-  int argc;
-  pic_value *argv, k, dyn_env;
-  struct context *cxt, *c;
-  int i;
-
-  pic_get_args(pic, "*", &argc, &argv);
-
-  cxt = pic_data(pic, pic_closure_ref(pic, 0));
-
-  /* check if continuation is alive */
-  for (c = pic->cxt; c != NULL; c = c->prev) {
-    if (c == cxt) {
-      break;
-    }
-  }
-  if (c == NULL) {
-    pic_error(pic, "calling dead escape continuation", 0);
-  }
-
-  k = pic_closure_ref(pic, 1);
-  dyn_env = pic_closure_ref(pic, 2);
-
-#define MKCALLK(argc)                                                   \
-  (cxt->tmpcode[0] = OP_CALL, cxt->tmpcode[1] = (argc), cxt->tmpcode)
-
-  cxt->pc = MKCALLK(argc);
-  cxt->sp = pic_make_frame_unsafe(pic, argc + 2);
-  cxt->sp->regs[0] = k;
-  for (i = 0; i < argc; ++i) {
-    cxt->sp->regs[i + 1] = argv[i];
-  }
-  pic->cxt = cxt;
-
-  pic->dyn_env = dyn_env;
-
-  longjmp(cxt->jmp, 1);
-  PIC_UNREACHABLE();
-}
-
-pic_value
-pic_make_cont(pic_state *pic, pic_value k)
-{
-  static const pic_data_type cxt_type = { "cxt", NULL };
-  return pic_lambda(pic, cont_call, 3, pic_data_value(pic, pic->cxt, &cxt_type), k, pic->dyn_env);
-}
-
-static pic_value
-pic_cont_callcc(pic_state *pic)
-{
-  pic_value f, args[1];
-
-  pic_get_args(pic, "l", &f);
-
-  args[0] = pic_make_cont(pic, pic->cxt->fp->regs[1]);
-  return pic_applyk(pic, f, 1, args);
-}
-
-#endif  /* PIC_USE_CALCC */
-
-static pic_value
-applyk(pic_state *pic, pic_value proc, pic_value cont, int argc, pic_value *argv)
-{
-  int i;
-
-#define MKCALL(argc)                                                    \
-  (pic->cxt->tmpcode[0] = OP_CALL, pic->cxt->tmpcode[1] = (argc), pic->cxt->tmpcode)
-
-  pic->cxt->pc = MKCALL(argc + 1);
-  pic->cxt->sp = pic_make_frame_unsafe(pic, argc + 3);
-  pic->cxt->sp->regs[0] = proc;
-  pic->cxt->sp->regs[1] = cont;
-  for (i = 0; i < argc; ++i) {
-    pic->cxt->sp->regs[i + 2] = argv[i];
-  }
-  return pic_invalid_value(pic);
-}
-
-static pic_value
-valuesk(pic_state *pic, int argc, pic_value *argv)
-{
-  int i;
-
-  pic->cxt->pc = MKCALL(argc);
-  pic->cxt->sp = pic_make_frame_unsafe(pic, argc + 2);
-  pic->cxt->sp->regs[0] = pic->cxt->fp->regs[1];
-  for (i = 0; i < argc; ++i) {
-    pic->cxt->sp->regs[i + 1] = argv[i];
-  }
-  return pic_invalid_value(pic);
-}
-
-pic_value
-pic_values(pic_state *pic, int n, ...)
-{
-  va_list ap;
-  pic_value ret;
-
-  va_start(ap, n);
-  ret = pic_vvalues(pic, n, ap);
-  va_end(ap);
-  return ret;
-}
-
-pic_value
-pic_vvalues(pic_state *pic, int n, va_list ap)
-{
-  pic_value *retv;
-  int i;
-
-  if (n == 1) {
-    return va_arg(ap, pic_value);
-  }
-  retv = pic_alloca(pic, sizeof(pic_value) * n);
-  for (i = 0; i < n; ++i) {
-    retv[i] = va_arg(ap, pic_value);
-  }
-  return valuesk(pic, n, retv);
-}
-
-static pic_value
-pic_cont_values(pic_state *pic)
-{
-  int argc;
-  pic_value *argv;
-
-  pic_get_args(pic, "*", &argc, &argv);
-
-  if (argc == 1) {
-    return argv[0];
-  }
-  return valuesk(pic, argc, argv);
-}
-
-static pic_value
-receive_call(pic_state *pic)
-{
-  int argc = pic->cxt->pc[1];
-  pic_value *args = &pic->cxt->fp->regs[1], consumer, cont;
-
-  /* receive_call is an inhabitant in the continuation side.
-     You can not use pic_get_args since it implicitly consumes the first argument. */
-
-  consumer = pic_closure_ref(pic, 0);
-  cont = pic_closure_ref(pic, 1);
-
-  return applyk(pic, consumer, cont, argc, args);
-}
-
-static pic_value
-pic_cont_call_with_values(pic_state *pic)
-{
-  pic_value producer, consumer, k;
-
-  pic_get_args(pic, "ll", &producer, &consumer);
-
-  k = pic_lambda(pic, receive_call, 2, consumer, pic->cxt->fp->regs[1]);
-
-  return applyk(pic, producer, k, 0, NULL);
-}
-
-void
-pic_init_cont(pic_state *pic)
-{
-#if PIC_USE_CALLCC
-  pic_defun(pic, "call-with-current-continuation", pic_cont_callcc);
-  pic_defun(pic, "call/cc", pic_cont_callcc);
-#endif
-  pic_defun(pic, "values", pic_cont_values);
-  pic_defun(pic, "call-with-values", pic_cont_call_with_values);
-}
diff --git a/lib/ext/cont.c b/lib/ext/cont.c
new file mode 100644
index 00000000..91f613d7
--- /dev/null
+++ b/lib/ext/cont.c
@@ -0,0 +1,78 @@
+/**
+ * See Copyright Notice in picrin.h
+ */
+
+#include "picrin.h"
+#include "../object.h"
+#include "../state.h"
+
+#if PIC_USE_CALLCC
+
+static pic_value
+cont_call(pic_state *pic)
+{
+  int argc;
+  pic_value *argv, k, dyn_env;
+  struct context *cxt, *c;
+  int i;
+
+  pic_get_args(pic, "*", &argc, &argv);
+
+  cxt = pic_data(pic, pic_closure_ref(pic, 0));
+
+  /* check if continuation is alive */
+  for (c = pic->cxt; c != NULL; c = c->prev) {
+    if (c == cxt) {
+      break;
+    }
+  }
+  if (c == NULL) {
+    pic_error(pic, "calling dead escape continuation", 0);
+  }
+
+  k = pic_closure_ref(pic, 1);
+  dyn_env = pic_closure_ref(pic, 2);
+
+#define MKCALLK(argc)                                                   \
+  (cxt->tmpcode[0] = OP_CALL, cxt->tmpcode[1] = (argc), cxt->tmpcode)
+
+  cxt->pc = MKCALLK(argc);
+  cxt->sp = pic_make_frame_unsafe(pic, argc + 2);
+  cxt->sp->regs[0] = k;
+  for (i = 0; i < argc; ++i) {
+    cxt->sp->regs[i + 1] = argv[i];
+  }
+  pic->cxt = cxt;
+
+  pic->dyn_env = dyn_env;
+
+  longjmp(cxt->jmp, 1);
+  PIC_UNREACHABLE();
+}
+
+pic_value
+pic_make_cont(pic_state *pic, pic_value k)
+{
+  static const pic_data_type cxt_type = { "cxt", NULL };
+  return pic_lambda(pic, cont_call, 3, pic_data_value(pic, pic->cxt, &cxt_type), k, pic->dyn_env);
+}
+
+static pic_value
+pic_cont_callcc(pic_state *pic)
+{
+  pic_value f, args[1];
+
+  pic_get_args(pic, "l", &f);
+
+  args[0] = pic_make_cont(pic, pic->cxt->fp->regs[1]);
+  return pic_applyk(pic, f, 1, args);
+}
+
+void
+pic_init_cont(pic_state *pic)
+{
+  pic_defun(pic, "call-with-current-continuation", pic_cont_callcc);
+  pic_defun(pic, "call/cc", pic_cont_callcc);
+}
+
+#endif  /* PIC_USE_CALCC */
diff --git a/lib/proc.c b/lib/proc.c
index 2a4b9b50..1cfd11e2 100644
--- a/lib/proc.c
+++ b/lib/proc.c
@@ -682,30 +682,72 @@ pic_apply(pic_state *pic, pic_value proc, int argc, pic_value *argv)
   } VM_LOOP_END
 }
 
-pic_value
-pic_applyk(pic_state *pic, pic_value proc, int argc, pic_value *args)
+static pic_value
+applyk(pic_state *pic, pic_value proc, pic_value cont, int argc, pic_value *argv)
 {
-  const code_t *pc;
-  struct frame *sp;
+  int i;
 
 #define MKCALLK(argc)                                                   \
   (pic->cxt->tmpcode[0] = OP_CALL, pic->cxt->tmpcode[1] = (argc), pic->cxt->tmpcode)
 
-  pc = MKCALLK(argc + 1);
-  sp = pic_make_frame_unsafe(pic, argc + 3);
-  sp->regs[0] = proc;
-  sp->regs[1] = GET_CONT(pic);
-  if (argc != 0) {
-    int i;
-    for (i = 0; i < argc; ++i) {
-      sp->regs[i + 2] = args[i];
-    }
+  pic->cxt->pc = MKCALLK(argc + 1);
+  pic->cxt->sp = pic_make_frame_unsafe(pic, argc + 3);
+  pic->cxt->sp->regs[0] = proc;
+  pic->cxt->sp->regs[1] = cont;
+  for (i = 0; i < argc; ++i) {
+    pic->cxt->sp->regs[i + 2] = argv[i];
   }
-  pic->cxt->pc = pc;
-  pic->cxt->sp = sp;
   return pic_invalid_value(pic);
 }
 
+pic_value
+pic_applyk(pic_state *pic, pic_value proc, int argc, pic_value *args)
+{
+  return applyk(pic, proc, GET_CONT(pic), argc, args);
+}
+
+static pic_value
+valuesk(pic_state *pic, int argc, pic_value *argv)
+{
+  int i;
+
+  pic->cxt->pc = MKCALLK(argc);
+  pic->cxt->sp = pic_make_frame_unsafe(pic, argc + 2);
+  pic->cxt->sp->regs[0] = pic->cxt->fp->regs[1];
+  for (i = 0; i < argc; ++i) {
+    pic->cxt->sp->regs[i + 1] = argv[i];
+  }
+  return pic_invalid_value(pic);
+}
+
+pic_value
+pic_values(pic_state *pic, int n, ...)
+{
+  va_list ap;
+  pic_value ret;
+
+  va_start(ap, n);
+  ret = pic_vvalues(pic, n, ap);
+  va_end(ap);
+  return ret;
+}
+
+pic_value
+pic_vvalues(pic_state *pic, int n, va_list ap)
+{
+  pic_value *retv;
+  int i;
+
+  if (n == 1) {
+    return va_arg(ap, pic_value);
+  }
+  retv = pic_alloca(pic, sizeof(pic_value) * n);
+  for (i = 0; i < n; ++i) {
+    retv[i] = va_arg(ap, pic_value);
+  }
+  return valuesk(pic, n, retv);
+}
+
 static pic_value
 pic_proc_make_procedure(pic_state *pic)
 {
@@ -758,10 +800,53 @@ pic_proc_apply(pic_state *pic)
   return pic_applyk(pic, proc, n, arg_list);
 }
 
+static pic_value
+pic_proc_values(pic_state *pic)
+{
+  int argc;
+  pic_value *argv;
+
+  pic_get_args(pic, "*", &argc, &argv);
+
+  if (argc == 1) {
+    return argv[0];
+  }
+  return valuesk(pic, argc, argv);
+}
+
+static pic_value
+receive_call(pic_state *pic)
+{
+  int argc = pic->cxt->pc[1];
+  pic_value *args = &pic->cxt->fp->regs[1], consumer, cont;
+
+  /* receive_call is an inhabitant in the continuation side.
+     You can not use pic_get_args since it implicitly consumes the first argument. */
+
+  consumer = pic_closure_ref(pic, 0);
+  cont = pic_closure_ref(pic, 1);
+
+  return applyk(pic, consumer, cont, argc, args);
+}
+
+static pic_value
+pic_proc_call_with_values(pic_state *pic)
+{
+  pic_value producer, consumer, k;
+
+  pic_get_args(pic, "ll", &producer, &consumer);
+
+  k = pic_lambda(pic, receive_call, 2, consumer, pic->cxt->fp->regs[1]);
+
+  return applyk(pic, producer, k, 0, NULL);
+}
+
 void
 pic_init_proc(pic_state *pic)
 {
   pic_defun(pic, "make-procedure", pic_proc_make_procedure);
   pic_defun(pic, "procedure?", pic_proc_proc_p);
   pic_defun(pic, "apply", pic_proc_apply);
+  pic_defun(pic, "values", pic_proc_values);
+  pic_defun(pic, "call-with-values", pic_proc_call_with_values);
 }
diff --git a/lib/state.c b/lib/state.c
index 04eb290a..dc017ce6 100644
--- a/lib/state.c
+++ b/lib/state.c
@@ -127,7 +127,6 @@ pic_init_core(pic_state *pic)
   pic_init_symbol(pic); DONE;
   pic_init_vector(pic); DONE;
   pic_init_blob(pic); DONE;
-  pic_init_cont(pic); DONE;
   pic_init_char(pic); DONE;
   pic_init_error(pic); DONE;
   pic_init_str(pic); DONE;
@@ -137,6 +136,9 @@ pic_init_core(pic_state *pic)
   pic_init_weak(pic); DONE;
   pic_init_state(pic); DONE;
 
+#if PIC_USE_CALLCC
+  pic_init_cont(pic); DONE;
+#endif
 #if PIC_USE_READ
   pic_init_read(pic); DONE;
 #endif