diff --git a/extlib/benz/bool.c b/extlib/benz/bool.c
index 35ec40d3..09ea02a2 100644
--- a/extlib/benz/bool.c
+++ b/extlib/benz/bool.c
@@ -94,7 +94,7 @@ internal_equal_p(pic_state *pic, pic_value x, pic_value y, int depth, khash_t(m)
 
   switch (pic_type(pic, x)) {
   case PIC_TYPE_ID: {
-    pic_id *id1, *id2;
+    identifier *id1, *id2;
     pic_value s1, s2;
 
     id1 = pic_id_ptr(pic, x);
diff --git a/extlib/benz/dict.c b/extlib/benz/dict.c
index cfbf73ff..a4b209c4 100644
--- a/extlib/benz/dict.c
+++ b/extlib/benz/dict.c
@@ -6,7 +6,7 @@
 #include "picrin/extra.h"
 #include "picrin/private/object.h"
 
-KHASH_DEFINE(dict, pic_sym *, pic_value, kh_ptr_hash_func, kh_ptr_hash_equal)
+KHASH_DEFINE(dict, symbol *, pic_value, kh_ptr_hash_func, kh_ptr_hash_equal)
 
 pic_value
 pic_make_dict(pic_state *pic)
diff --git a/extlib/benz/gc.c b/extlib/benz/gc.c
index 985ea214..b5030ae0 100644
--- a/extlib/benz/gc.c
+++ b/extlib/benz/gc.c
@@ -620,7 +620,7 @@ gc_sweep_phase(pic_state *pic)
   int it;
   khash_t(weak) *h;
   khash_t(oblist) *s = &pic->oblist;
-  pic_sym *sym;
+  symbol *sym;
   struct pic_object *obj;
   size_t total = 0, inuse = 0;
 
diff --git a/extlib/benz/include/picrin/private/object.h b/extlib/benz/include/picrin/private/object.h
index 6f50bdfb..e6e2035c 100644
--- a/extlib/benz/include/picrin/private/object.h
+++ b/extlib/benz/include/picrin/private/object.h
@@ -11,11 +11,11 @@ extern "C" {
 
 #include "picrin/private/khash.h"
 
-typedef struct pic_identifier pic_id;
-typedef pic_id pic_sym;
+typedef struct pic_identifier identifier;
+typedef identifier symbol;
 
-KHASH_DECLARE(env, pic_id *, pic_sym *)
-KHASH_DECLARE(dict, pic_sym *, pic_value)
+KHASH_DECLARE(env, identifier *, symbol *)
+KHASH_DECLARE(dict, symbol *, pic_value)
 KHASH_DECLARE(weak, struct pic_object *, pic_value)
 
 #define PIC_OBJECT_HEADER			\
@@ -119,7 +119,7 @@ struct pic_record {
 
 struct pic_error {
   PIC_OBJECT_HEADER
-  pic_sym *type;
+  symbol *type;
   struct pic_string *msg;
   pic_value irrs;
   struct pic_string *stack;
@@ -140,8 +140,8 @@ struct pic_checkpoint {
 
 struct pic_object *pic_obj_ptr(pic_value);
 
-#define pic_id_ptr(pic, o) (assert(pic_id_p(pic, o)), (pic_id *)pic_obj_ptr(o))
-#define pic_sym_ptr(pic, o) (assert(pic_sym_p(pic, o)), (pic_sym *)pic_obj_ptr(o))
+#define pic_id_ptr(pic, o) (assert(pic_id_p(pic, o)), (identifier *)pic_obj_ptr(o))
+#define pic_sym_ptr(pic, o) (assert(pic_sym_p(pic, o)), (symbol *)pic_obj_ptr(o))
 #define pic_str_ptr(pic, o) (assert(pic_str_p(pic, o)), (struct pic_string *)pic_obj_ptr(o))
 #define pic_blob_ptr(pic, o) (assert(pic_blob_p(pic, o)), (struct pic_blob *)pic_obj_ptr(o))
 #define pic_pair_ptr(pic, o) (assert(pic_pair_p(pic, o)), (struct pic_pair *)pic_obj_ptr(o))
diff --git a/extlib/benz/macro.c b/extlib/benz/macro.c
index b1e710d5..8028f6cf 100644
--- a/extlib/benz/macro.c
+++ b/extlib/benz/macro.c
@@ -7,7 +7,7 @@
 #include "picrin/private/object.h"
 #include "picrin/private/state.h"
 
-KHASH_DEFINE(env, pic_id *, pic_sym *, kh_ptr_hash_func, kh_ptr_hash_equal)
+KHASH_DEFINE(env, identifier *, symbol *, kh_ptr_hash_func, kh_ptr_hash_equal)
 
 pic_value
 pic_make_env(pic_state *pic, pic_value up)
diff --git a/extlib/benz/symbol.c b/extlib/benz/symbol.c
index 8ebd3913..3f40ef43 100644
--- a/extlib/benz/symbol.c
+++ b/extlib/benz/symbol.c
@@ -10,13 +10,13 @@
 #define kh_pic_str_hash(a) (pic_str_hash(pic, pic_obj_value(a)))
 #define kh_pic_str_cmp(a, b) (pic_str_cmp(pic, pic_obj_value(a), pic_obj_value(b)) == 0)
 
-KHASH_DEFINE(oblist, struct pic_string *, pic_sym *, kh_pic_str_hash, kh_pic_str_cmp)
+KHASH_DEFINE(oblist, struct pic_string *, symbol *, kh_pic_str_hash, kh_pic_str_cmp)
 
 pic_value
 pic_intern(pic_state *pic, pic_value str)
 {
   khash_t(oblist) *h = &pic->oblist;
-  pic_sym *sym;
+  symbol *sym;
   int it;
   int ret;
 
@@ -29,7 +29,7 @@ pic_intern(pic_state *pic, pic_value str)
 
   kh_val(h, it) = NULL;         /* dummy */
 
-  sym = (pic_sym *)pic_obj_alloc(pic, offsetof(pic_sym, env), PIC_TYPE_SYMBOL);
+  sym = (symbol *)pic_obj_alloc(pic, offsetof(symbol, env), PIC_TYPE_SYMBOL);
   sym->u.str = pic_str_ptr(pic, str);
   kh_val(h, it) = sym;
 
@@ -39,9 +39,9 @@ pic_intern(pic_state *pic, pic_value str)
 pic_value
 pic_make_identifier(pic_state *pic, pic_value base, pic_value env)
 {
-  pic_id *id;
+  identifier *id;
 
-  id = (pic_id *)pic_obj_alloc(pic, sizeof(pic_id), PIC_TYPE_ID);
+  id = (identifier *)pic_obj_alloc(pic, sizeof(identifier), PIC_TYPE_ID);
   id->u.id = pic_id_ptr(pic, base);
   id->env = pic_env_ptr(pic, env);