diff --git a/extlib/benz/include/picrin.h b/extlib/benz/include/picrin.h
index b1483dd3..84df7381 100644
--- a/extlib/benz/include/picrin.h
+++ b/extlib/benz/include/picrin.h
@@ -53,7 +53,6 @@ typedef struct {
 
 struct pic_object;
 struct pic_symbol;
-struct pic_pair;
 struct pic_string;
 struct pic_blob;
 struct pic_proc;
@@ -64,7 +63,6 @@ struct pic_data;
 
 typedef struct pic_symbol pic_sym;
 typedef struct pic_id pic_id;
-typedef struct pic_pair pic_pair;
 
 typedef void *(*pic_allocf)(void *userdata, void *ptr, size_t n);
 
diff --git a/extlib/benz/include/picrin/object.h b/extlib/benz/include/picrin/object.h
index 08acd36c..7e71ef38 100644
--- a/extlib/benz/include/picrin/object.h
+++ b/extlib/benz/include/picrin/object.h
@@ -120,11 +120,11 @@ struct pic_port {
   xFILE *file;
 };
 
+#define pic_pair_ptr(pic, o) ((struct pic_pair *)pic_obj_ptr(o))
 #define pic_vec_ptr(pic, o) ((struct pic_vector *)pic_obj_ptr(o))
 #define pic_dict_ptr(pic, v) ((struct pic_dict *)pic_obj_ptr(v))
 #define pic_sym_ptr(v) ((pic_sym *)pic_obj_ptr(v))
 #define pic_id_ptr(v) ((pic_id *)pic_obj_ptr(v))
-#define pic_pair_ptr(o) ((struct pic_pair *)pic_obj_ptr(o))
 #define pic_blob_ptr(v) ((struct pic_blob *)pic_obj_ptr(v))
 #define pic_str_ptr(o) ((struct pic_string *)pic_obj_ptr(o))
 #define pic_weak_ptr(v) ((struct pic_weak *)pic_obj_ptr(v))
diff --git a/extlib/benz/pair.c b/extlib/benz/pair.c
index 6507c49e..a58b6cc4 100644
--- a/extlib/benz/pair.c
+++ b/extlib/benz/pair.c
@@ -20,53 +20,37 @@ pic_cons(pic_state *pic, pic_value car, pic_value cdr)
 pic_value
 pic_car(pic_state *pic, pic_value obj)
 {
-  struct pic_pair *pair;
-
   if (! pic_pair_p(pic, obj)) {
     pic_errorf(pic, "car: pair required, but got ~s", obj);
   }
-  pair = pic_pair_ptr(obj);
-
-  return pair->car;
+  return pic_pair_ptr(pic, obj)->car;
 }
 
 pic_value
 pic_cdr(pic_state *pic, pic_value obj)
 {
-  struct pic_pair *pair;
-
   if (! pic_pair_p(pic, obj)) {
     pic_errorf(pic, "cdr: pair required, but got ~s", obj);
   }
-  pair = pic_pair_ptr(obj);
-
-  return pair->cdr;
+  return pic_pair_ptr(pic, obj)->cdr;
 }
 
 void
 pic_set_car(pic_state *pic, pic_value obj, pic_value val)
 {
-  struct pic_pair *pair;
-
   if (! pic_pair_p(pic, obj)) {
     pic_errorf(pic, "pair required");
   }
-  pair = pic_pair_ptr(obj);
-
-  pair->car = val;
+  pic_pair_ptr(pic, obj)->car = val;
 }
 
 void
 pic_set_cdr(pic_state *pic, pic_value obj, pic_value val)
 {
-  struct pic_pair *pair;
-
   if (! pic_pair_p(pic, obj)) {
     pic_errorf(pic, "pair required");
   }
-  pair = pic_pair_ptr(obj);
-
-  pair->cdr = val;
+  pic_pair_ptr(pic, obj)->cdr = val;
 }
 
 pic_value
@@ -107,7 +91,7 @@ pic_list_p(pic_state *pic, pic_value obj)
     /* advance rapid fast-forward; runs 2x faster than local */
     for (i = 0; i < 2; ++i) {
       if (pic_pair_p(pic, rapid)) {
-        rapid = pic_pair_ptr(rapid)->cdr;
+        rapid = pic_pair_ptr(pic, rapid)->cdr;
       }
       else {
         return pic_nil_p(pic, rapid);
@@ -115,7 +99,7 @@ pic_list_p(pic_state *pic, pic_value obj)
     }
 
     /* advance local */
-    local = pic_pair_ptr(local)->cdr;
+    local = pic_pair_ptr(pic, local)->cdr;
 
     if (pic_eq_p(pic, local, rapid)) {
       return false;
@@ -169,7 +153,7 @@ pic_list_ref(pic_state *pic, pic_value list, int i)
 void
 pic_list_set(pic_state *pic, pic_value list, int i, pic_value obj)
 {
-  pic_pair_ptr(pic_list_tail(pic, list, i))->car = obj;
+  pic_pair_ptr(pic, pic_list_tail(pic, list, i))->car = obj;
 }
 
 pic_value
diff --git a/extlib/benz/read.c b/extlib/benz/read.c
index 2a7c99e5..4f26f86f 100644
--- a/extlib/benz/read.c
+++ b/extlib/benz/read.c
@@ -622,8 +622,8 @@ read_label_set(pic_state *pic, xFILE *file, int i)
       kh_val(h, it) = val = pic_cons(pic, pic_undef_value(pic), pic_undef_value(pic));
 
       tmp = read(pic, file, c);
-      pic_pair_ptr(val)->car = pic_car(pic, tmp);
-      pic_pair_ptr(val)->cdr = pic_cdr(pic, tmp);
+      pic_pair_ptr(pic, val)->car = pic_car(pic, tmp);
+      pic_pair_ptr(pic, val)->cdr = pic_cdr(pic, tmp);
 
       return val;
     }
diff --git a/extlib/benz/write.c b/extlib/benz/write.c
index a65dc804..228bc3d9 100644
--- a/extlib/benz/write.c
+++ b/extlib/benz/write.c
@@ -119,7 +119,7 @@ write_float(pic_state *pic, double f, xFILE *file)
 static void write_core(struct writer_control *p, pic_value);
 
 static void
-write_pair_help(struct writer_control *p, struct pic_pair *pair)
+write_pair_help(struct writer_control *p, pic_value pair)
 {
   pic_state *pic = p->pic;
   khash_t(l) *lh = &p->labels;
@@ -127,18 +127,18 @@ write_pair_help(struct writer_control *p, struct pic_pair *pair)
   khiter_t it;
   int ret;
 
-  write_core(p, pair->car);
+  write_core(p, pic_car(pic, pair));
 
-  if (pic_nil_p(pic, pair->cdr)) {
+  if (pic_nil_p(pic, pic_cdr(pic, pair))) {
     return;
   }
-  else if (pic_pair_p(pic, pair->cdr)) {
+  else if (pic_pair_p(pic, pic_cdr(pic, pair))) {
 
     /* shared objects */
-    if ((it = kh_get(l, lh, pic_obj_ptr(pair->cdr))) != kh_end(lh) && kh_val(lh, it) != -1) {
+    if ((it = kh_get(l, lh, pic_obj_ptr(pic_cdr(pic, pair)))) != kh_end(lh) && kh_val(lh, it) != -1) {
       xfprintf(pic, p->file, " . ");
 
-      kh_put(v, vh, pic_obj_ptr(pair->cdr), &ret);
+      kh_put(v, vh, pic_obj_ptr(pic_cdr(pic, pair)), &ret);
       if (ret == 0) {           /* if exists */
         xfprintf(pic, p->file, "#%d#", kh_val(lh, it));
         return;
@@ -149,11 +149,11 @@ write_pair_help(struct writer_control *p, struct pic_pair *pair)
       xfprintf(pic, p->file, " ");
     }
 
-    write_pair_help(p, pic_pair_ptr(pair->cdr));
+    write_pair_help(p, pic_cdr(pic, pair));
 
     if (p->op == OP_WRITE) {
-      if ((it = kh_get(l, lh, pic_obj_ptr(pair->cdr))) != kh_end(lh) && kh_val(lh, it) != -1) {
-        it = kh_get(v, vh, pic_obj_ptr(pair->cdr));
+      if ((it = kh_get(l, lh, pic_obj_ptr(pic_cdr(pic, pair)))) != kh_end(lh) && kh_val(lh, it) != -1) {
+        it = kh_get(v, vh, pic_obj_ptr(pic_cdr(pic, pair)));
         kh_del(v, vh, it);
       }
     }
@@ -161,57 +161,57 @@ write_pair_help(struct writer_control *p, struct pic_pair *pair)
   }
   else {
     xfprintf(pic, p->file, " . ");
-    write_core(p, pair->cdr);
+    write_core(p, pic_cdr(pic, pair));
   }
 }
 
 static void
-write_pair(struct writer_control *p, struct pic_pair *pair)
+write_pair(struct writer_control *p, pic_value pair)
 {
   pic_state *pic = p->pic;
   xFILE *file = p->file;
   pic_sym *tag;
 
-  if (pic_pair_p(pic, pair->cdr) && pic_nil_p(pic, pic_cdr(pic, pair->cdr)) && pic_sym_p(pic, pair->car)) {
-    tag = pic_sym_ptr(pair->car);
+  if (pic_pair_p(pic, pic_cdr(pic, pair)) && pic_nil_p(pic, pic_cddr(pic, pair)) && pic_sym_p(pic, pic_car(pic, pair))) {
+    tag = pic_sym_ptr(pic_car(pic, pair));
     if (tag == pic->sQUOTE) {
       xfprintf(pic, file, "'");
-      write_core(p, pic_car(pic, pair->cdr));
+      write_core(p, pic_cadr(pic, pair));
       return;
     }
     else if (tag == pic->sUNQUOTE) {
       xfprintf(pic, file, ",");
-      write_core(p, pic_car(pic, pair->cdr));
+      write_core(p, pic_cadr(pic, pair));
       return;
     }
     else if (tag == pic->sUNQUOTE_SPLICING) {
       xfprintf(pic, file, ",@");
-      write_core(p, pic_car(pic, pair->cdr));
+      write_core(p, pic_cadr(pic, pair));
       return;
     }
     else if (tag == pic->sQUASIQUOTE) {
       xfprintf(pic, file, "`");
-      write_core(p, pic_car(pic, pair->cdr));
+      write_core(p, pic_cadr(pic, pair));
       return;
     }
     else if (tag == pic->sSYNTAX_QUOTE) {
       xfprintf(pic, file, "#'");
-      write_core(p, pic_car(pic, pair->cdr));
+      write_core(p, pic_cadr(pic, pair));
       return;
     }
     else if (tag == pic->sSYNTAX_UNQUOTE) {
       xfprintf(pic, file, "#,");
-      write_core(p, pic_car(pic, pair->cdr));
+      write_core(p, pic_cadr(pic, pair));
       return;
     }
     else if (tag == pic->sSYNTAX_UNQUOTE_SPLICING) {
       xfprintf(pic, file, "#,@");
-      write_core(p, pic_car(pic, pair->cdr));
+      write_core(p, pic_cadr(pic, pair));
       return;
     }
     else if (tag == pic->sSYNTAX_QUASIQUOTE) {
       xfprintf(pic, file, "#`");
-      write_core(p, pic_car(pic, pair->cdr));
+      write_core(p, pic_cadr(pic, pair));
       return;
     }
   }
@@ -312,7 +312,7 @@ write_core(struct writer_control *p, pic_value obj)
     write_str(pic, pic_str_ptr(obj), file, p->mode);
     break;
   case PIC_TYPE_PAIR:
-    write_pair(p, pic_pair_ptr(obj));
+    write_pair(p, obj);
     break;
   case PIC_TYPE_VECTOR:
     write_vec(p, obj);