diff --git a/contrib/10.callcc/callcc.c b/contrib/10.callcc/callcc.c
deleted file mode 100644
index 07bd8940..00000000
--- a/contrib/10.callcc/callcc.c
+++ /dev/null
@@ -1,256 +0,0 @@
-#include "picrin.h"
-#include "object.h"
-#include "state.h"
-
-struct fullcont {
-  jmp_buf jmp;
-
-  struct cont *prev_jmp;
-
-  struct checkpoint *cp;
-
-  char *stk_pos, *stk_ptr;
-  ptrdiff_t stk_len;
-
-  pic_value *st_ptr;
-  size_t sp_offset;
-  ptrdiff_t st_len;
-
-  struct callinfo *ci_ptr;
-  size_t ci_offset;
-  ptrdiff_t ci_len;
-
-  const struct code *ip;
-
-  struct object **arena;
-  size_t arena_size, arena_idx;
-
-  int retc;
-  pic_value *retv;
-};
-
-char *picrin_native_stack_start;
-
-static void
-cont_dtor(pic_state *pic, void *data)
-{
-  struct fullcont *cont = data;
-
-  pic_free(pic, cont->stk_ptr);
-  pic_free(pic, cont->st_ptr);
-  pic_free(pic, cont->ci_ptr);
-  pic_free(pic, cont->arena);
-  pic_free(pic, cont);
-}
-
-static void
-cont_mark(pic_state *pic, void *data, void (*mark)(pic_state *, pic_value))
-{
-  struct fullcont *cont = data;
-  struct checkpoint *cp;
-  pic_value *stack;
-  struct callinfo *ci;
-  size_t i;
-
-  /* checkpoint */
-  for (cp = cont->cp; cp != NULL; cp = cp->prev) {
-    if (cp->in) {
-      mark(pic, obj_value(pic, cp->in));
-    }
-    if (cp->out) {
-      mark(pic, obj_value(pic, cp->out));
-    }
-  }
-
-  /* stack */
-  for (stack = cont->st_ptr; stack != cont->st_ptr + cont->sp_offset; ++stack) {
-    mark(pic, *stack);
-  }
-
-  /* callinfo */
-  for (ci = cont->ci_ptr + cont->ci_offset; ci != cont->ci_ptr; --ci) {
-    if (ci->cxt) {
-      mark(pic, obj_value(pic, ci->cxt));
-    }
-  }
-
-  /* arena */
-  for (i = 0; i < cont->arena_idx; ++i) {
-    mark(pic, obj_value(pic, cont->arena[i]));
-  }
-}
-
-static const pic_data_type cont_type = { "continuation", cont_dtor, cont_mark };
-
-static void save_cont(pic_state *, struct fullcont *);
-static void restore_cont(pic_state *, struct fullcont *);
-
-#if __GNUC__
-# define NOINLINE __attribute__ ((noinline))
-#else
-# define NOINLINE
-#endif
-
-static ptrdiff_t NOINLINE
-native_stack_length(char **pos)
-{
-  char t;
-
-  *pos = (picrin_native_stack_start > &t)
-    ? &t
-    : picrin_native_stack_start;
-
-  return (picrin_native_stack_start > &t)
-    ? picrin_native_stack_start - &t
-    : &t - picrin_native_stack_start;
-}
-
-static void NOINLINE
-save_cont(pic_state *pic, struct fullcont *cont)
-{
-  void pic_vm_tear_off(pic_state *);
-  char *pos;
-
-  pic_vm_tear_off(pic);         /* tear off */
-
-  cont->prev_jmp = pic->cc;
-
-  cont->cp = pic->cp;
-
-  cont->stk_len = native_stack_length(&pos);
-  cont->stk_pos = pos;
-  assert(cont->stk_len > 0);
-  cont->stk_ptr = pic_malloc(pic, cont->stk_len);
-  memcpy(cont->stk_ptr, cont->stk_pos, cont->stk_len);
-
-  cont->sp_offset = pic->sp - pic->stbase;
-  cont->st_len = pic->stend - pic->stbase;
-  cont->st_ptr = pic_malloc(pic, sizeof(pic_value) * cont->st_len);
-  memcpy(cont->st_ptr, pic->stbase, sizeof(pic_value) * cont->st_len);
-
-  cont->ci_offset = pic->ci - pic->cibase;
-  cont->ci_len = pic->ciend - pic->cibase;
-  cont->ci_ptr = pic_malloc(pic, sizeof(struct callinfo) * cont->ci_len);
-  memcpy(cont->ci_ptr, pic->cibase, sizeof(struct callinfo) * cont->ci_len);
-
-  cont->ip = pic->ip;
-
-  cont->arena_idx = pic->arena_idx;
-  cont->arena_size = pic->arena_size;
-  cont->arena = pic_malloc(pic, sizeof(struct object *) * pic->arena_size);
-  memcpy(cont->arena, pic->arena, sizeof(struct object *) * pic->arena_size);
-
-  cont->retc = 0;
-  cont->retv = NULL;
-}
-
-static void NOINLINE
-native_stack_extend(pic_state *pic, struct fullcont *cont)
-{
-  pic_value v[1024];
-
-  memset(v, 0, sizeof v);
-
-  restore_cont(pic, cont);
-}
-
-PIC_NORETURN static void
-restore_cont(pic_state *pic, struct fullcont *cont)
-{
-  char v;
-  struct fullcont *tmp = cont;
-
-  if (&v < picrin_native_stack_start) {
-    if (&v > cont->stk_pos) native_stack_extend(pic, cont);
-  }
-  else {
-    if (&v < cont->stk_pos + cont->stk_len) native_stack_extend(pic, cont);
-  }
-
-  pic->cc = cont->prev_jmp;
-  pic->cp = cont->cp;
-
-  assert(pic->stend - pic->stbase >= cont->st_len);
-  memcpy(pic->stbase, cont->st_ptr, sizeof(pic_value) * cont->st_len);
-  pic->sp = pic->stbase + cont->sp_offset;
-  pic->stend = pic->stbase + cont->st_len;
-
-  assert(pic->ciend - pic->cibase >= cont->ci_len);
-  memcpy(pic->cibase, cont->ci_ptr, sizeof(struct callinfo) * cont->ci_len);
-  pic->ci = pic->cibase + cont->ci_offset;
-  pic->ciend = pic->cibase + cont->ci_len;
-
-  pic->ip = cont->ip;
-
-  assert(pic->arena_size >= cont->arena_size);
-  memcpy(pic->arena, cont->arena, sizeof(struct object *) * cont->arena_size);
-  pic->arena_size = cont->arena_size;
-  pic->arena_idx = cont->arena_idx;
-
-  memcpy(cont->stk_pos, cont->stk_ptr, cont->stk_len);
-
-  longjmp(tmp->jmp, 1);
-}
-
-PIC_NORETURN static pic_value
-cont_call(pic_state *pic)
-{
-  int argc, i;
-  pic_value *argv, *retv;
-  struct fullcont *cont;
-
-  pic_get_args(pic, "*", &argc, &argv);
-
-  retv = pic_alloca(pic, sizeof(pic_value) * argc);
-  for (i = 0; i < argc; ++i) {
-    retv[i] = argv[i];
-  }
-
-  cont = pic_data(pic, pic_closure_ref(pic, 0));
-  cont->retc = argc;
-  cont->retv = retv;
-
-  /* execute guard handlers */
-  pic_wind(pic, pic->cp, cont->cp);
-
-  restore_cont(pic, cont);
-}
-
-static pic_value
-pic_callcc(pic_state *pic, pic_value proc)
-{
-  struct fullcont *cont = pic_malloc(pic, sizeof(struct fullcont));
-
-  if (setjmp(cont->jmp) != 0) {
-    return pic_valuesk(pic, cont->retc, cont->retv);
-  } else {
-    pic_value c[1];
-
-    save_cont(pic, cont);
-
-    /* save the continuation object in proc */
-    c[0] = pic_lambda(pic, cont_call, 1, pic_data_value(pic, cont, &cont_type));
-
-    return pic_applyk(pic, proc, 1, c);
-  }
-}
-
-static pic_value
-pic_callcc_callcc(pic_state *pic)
-{
-  pic_value proc;
-
-  pic_get_args(pic, "l", &proc);
-
-  return pic_callcc(pic, proc);
-}
-
-#define pic_redefun(pic, lib, name, func)               \
-  pic_set(pic, lib, name, pic_lambda(pic, func, 0))
-
-void
-pic_init_callcc(pic_state *pic)
-{
-  pic_redefun(pic, "picrin.base", "call-with-current-continuation", pic_callcc_callcc);
-  pic_redefun(pic, "picrin.base", "call/cc", pic_callcc_callcc);
-}
diff --git a/contrib/10.callcc/nitro.mk b/contrib/10.callcc/nitro.mk
deleted file mode 100644
index 0779aa0f..00000000
--- a/contrib/10.callcc/nitro.mk
+++ /dev/null
@@ -1,2 +0,0 @@
-CONTRIB_INITS += callcc
-CONTRIB_SRCS += $(wildcard contrib/10.callcc/*.c)
diff --git a/contrib/30.regexp/src/regexp.c b/contrib/30.regexp/src/regexp.c
index c428ad1c..5a9972be 100644
--- a/contrib/30.regexp/src/regexp.c
+++ b/contrib/30.regexp/src/regexp.c
@@ -18,7 +18,7 @@ regexp_dtor(pic_state *pic, void *data)
   pic_free(pic, data);
 }
 
-static const pic_data_type regexp_type = { "regexp", regexp_dtor, NULL };
+static const pic_data_type regexp_type = { "regexp", regexp_dtor };
 
 static pic_value
 pic_regexp_regexp(pic_state *pic)
diff --git a/contrib/30.test/test.scm b/contrib/30.test/test.scm
index 76455882..e88d6a70 100644
--- a/contrib/30.test/test.scm
+++ b/contrib/30.test/test.scm
@@ -38,33 +38,54 @@
       ((test expected expr)
        (test expected expr equal?))
       ((test expected expr =)
-       (let ((res expr))
+       (begin
          (display "case ")
          (write counter)
-         (if (= res expected)
-           (begin
-             (display " PASS: ")
-             (write 'expr)
-             (display " equals ")
-             (write expected)
-             (display "")
-             (newline))
-           (begin
-             (set! failure-counter (+ failure-counter 1))
-             (let ((out (open-output-string)))
-               (display " FAIL: " out)
-               (write 'expr out)
-               (newline out)
-               (display "   expected " out)
-               (write expected out)
-               (display " but got " out)
-               (write res out)
-               (display "" out)
-               (newline out)
-               (let ((str (get-output-string out)))
-                 (set! fails (cons str fails))
-                 (display str)))))
-         (set! counter (+ counter 1))))))
+         (let ((res (call/cc
+                     (lambda (k)
+                       (with-exception-handler
+                        (lambda (e) (k (cons 'raised e)))
+                        (lambda ()
+                          (cons #f expr)))))))
+           (if (eq? (car res) 'raised)
+               (let ((out (open-output-string)))
+                 (display " ERROR: " out)
+                 (write 'expr out)
+                 (newline out)
+                 (display "   expected " out)
+                 (write expected out)
+                 (display " but got an error " out)
+                 (write (cdr res) out)
+                 (display "" out)
+                 (newline out)
+                 (let ((str (get-output-string out)))
+                   (set! fails (cons str fails))
+                   (display str)))
+               (let ((res (cdr res)))
+                 (if (= res expected)
+                     (begin
+                       (display " PASS: ")
+                       (write 'expr)
+                       (display " equals ")
+                       (write expected)
+                       (display "")
+                       (newline))
+                     (begin
+                       (set! failure-counter (+ failure-counter 1))
+                       (let ((out (open-output-string)))
+                         (display " FAIL: " out)
+                         (write 'expr out)
+                         (newline out)
+                         (display "   expected " out)
+                         (write expected out)
+                         (display " but got " out)
+                         (write res out)
+                         (display "" out)
+                         (newline out)
+                         (let ((str (get-output-string out)))
+                           (set! fails (cons str fails))
+                           (display str)))))))
+           (set! counter (+ counter 1)))))))
 
   (define-syntax test-values
     (syntax-rules ()
diff --git a/contrib/40.srfi/src/106.c b/contrib/40.srfi/src/106.c
index d8334fc8..cda947c3 100644
--- a/contrib/40.srfi/src/106.c
+++ b/contrib/40.srfi/src/106.c
@@ -45,7 +45,7 @@ socket_dtor(pic_state *pic, void *data)
   pic_free(pic, data);
 }
 
-static const pic_data_type socket_type = { "socket", socket_dtor, NULL };
+static const pic_data_type socket_type = { "socket", socket_dtor };
 
 static pic_value
 pic_socket_socket_p(pic_state *pic)
diff --git a/lib/cont.c b/lib/cont.c
index 3bc4333c..cc11dfbd 100644
--- a/lib/cont.c
+++ b/lib/cont.c
@@ -21,7 +21,7 @@ struct cont {
   struct cont *prev;
 };
 
-static const pic_data_type cont_type = { "cont", NULL, NULL };
+static const pic_data_type cont_type = { "cont", NULL };
 
 void
 pic_save_point(pic_state *pic, struct cont *cont, PIC_JMPBUF *jmp)
diff --git a/lib/gc.c b/lib/gc.c
index faf5e099..b455531e 100644
--- a/lib/gc.c
+++ b/lib/gc.c
@@ -191,7 +191,7 @@ pic_leave(pic_state *pic, size_t state)
 void *
 pic_alloca(pic_state *pic, size_t n)
 {
-  static const pic_data_type t = { "pic_alloca", pic_free, 0 };
+  static const pic_data_type t = { "pic_alloca", pic_free };
 
   return pic_data(pic, pic_data_value(pic, pic_malloc(pic, n), &t)); /* TODO optimize */
 }
@@ -399,9 +399,6 @@ gc_mark_object(pic_state *pic, struct object *obj)
     break;
   }
   case PIC_TYPE_DATA: {
-    if (obj->u.data.type->mark) {
-      obj->u.data.type->mark(pic, obj->u.data.data, gc_mark);
-    }
     break;
   }
   case PIC_TYPE_DICT: {
diff --git a/lib/include/picrin.h b/lib/include/picrin.h
index 6ca42b61..c2127de2 100644
--- a/lib/include/picrin.h
+++ b/lib/include/picrin.h
@@ -94,7 +94,6 @@ bool pic_equal_p(pic_state *, pic_value, pic_value);
 typedef struct {
   const char *type_name;
   void (*dtor)(pic_state *, void *);
-  void (*mark)(pic_state *, void *, void (*)(pic_state *, pic_value));
 } pic_data_type;
 
 bool pic_undef_p(pic_state *, pic_value); /* deprecated */
diff --git a/src/main.c b/src/main.c
index 9b6824d5..3733ba37 100644
--- a/src/main.c
+++ b/src/main.c
@@ -19,12 +19,9 @@ int picrin_argc;
 char **picrin_argv;
 char **picrin_envp;
 
-extern char *picrin_native_stack_start; /* for call/cc */
-
 int
 main(int argc, char *argv[], char **envp)
 {
-  char t;
   pic_state *pic;
   pic_value e;
   int status;
@@ -35,8 +32,6 @@ main(int argc, char *argv[], char **envp)
   picrin_argv = argv;
   picrin_envp = envp;
 
-  picrin_native_stack_start = &t;
-
   pic_try {
     pic_init_picrin(pic);