diff --git a/contrib/10.callcc/callcc.c b/contrib/10.callcc/callcc.c
index 0d48b6d3..7f102774 100644
--- a/contrib/10.callcc/callcc.c
+++ b/contrib/10.callcc/callcc.c
@@ -246,7 +246,7 @@ pic_callcc_full(pic_state *pic, struct pic_proc *proc)
     struct pic_proc *c;
 
     /* save the continuation object in proc */
-    c = pic_lambda(pic, cont_call, 1, pic_obj_value(pic_data_alloc(pic, &cont_type, cont)));
+    c = pic_lambda(pic, cont_call, 1, pic_obj_value(pic_data_value(pic, cont, &cont_type)));
 
     return pic_call(pic, proc, 1, pic_obj_value(c));
   }
@@ -269,7 +269,7 @@ pic_callcc_callcc(pic_state *pic)
     pic_value args[1];
 
     /* save the continuation object in proc */
-    c = pic_lambda(pic, cont_call, 1, pic_obj_value(pic_data_alloc(pic, &cont_type, cont)));
+    c = pic_lambda(pic, cont_call, 1, pic_obj_value(pic_data_value(pic, cont, &cont_type)));
 
     args[0] = pic_obj_value(c);
     return pic_applyk(pic, proc, 1, args);
diff --git a/contrib/20.r7rs/src/mutable-string.c b/contrib/20.r7rs/src/mutable-string.c
index db58687e..b00842df 100644
--- a/contrib/20.r7rs/src/mutable-string.c
+++ b/contrib/20.r7rs/src/mutable-string.c
@@ -13,7 +13,7 @@ pic_str_set(pic_state *pic, struct pic_string *str, int i, char c)
   buf[0] = c;
 
   x = pic_str_sub(pic, str, 0, i);
-  y = pic_make_str(pic, buf, 1);
+  y = pic_str_value(pic, buf, 1);
   z = pic_str_sub(pic, str, i + 1, pic_str_len(pic, str));
 
   tmp = pic_str_cat(pic, x, pic_str_cat(pic, y, z));
diff --git a/contrib/20.r7rs/src/system.c b/contrib/20.r7rs/src/system.c
index d53169aa..abcda8be 100644
--- a/contrib/20.r7rs/src/system.c
+++ b/contrib/20.r7rs/src/system.c
@@ -21,7 +21,7 @@ pic_system_cmdline(pic_state *pic)
   for (i = 0; i < picrin_argc; ++i) {
     size_t ai = pic_gc_arena_preserve(pic);
 
-    v = pic_cons(pic, pic_obj_value(pic_make_cstr(pic, picrin_argv[i])), v);
+    v = pic_cons(pic, pic_obj_value(pic_cstr_value(pic, picrin_argv[i])), v);
     pic_gc_arena_restore(pic, ai);
   }
 
@@ -88,7 +88,7 @@ pic_system_getenv(pic_state *pic)
   if (val == NULL)
     return pic_nil_value(pic);
   else
-    return pic_obj_value(pic_make_cstr(pic, val));
+    return pic_obj_value(pic_cstr_value(pic, val));
 }
 
 static pic_value
@@ -111,8 +111,8 @@ pic_system_getenvs(pic_state *pic)
     for (i = 0; (*envp)[i] != '='; ++i)
       ;
 
-    key = pic_make_str(pic, *envp, i);
-    val = pic_make_cstr(pic, getenv(pic_str_cstr(pic, key)));
+    key = pic_str_value(pic, *envp, i);
+    val = pic_cstr_value(pic, getenv(pic_str(pic, key)));
 
     /* push */
     data = pic_acons(pic, pic_obj_value(key), pic_obj_value(val), data);
diff --git a/contrib/30.readline/src/readline.c b/contrib/30.readline/src/readline.c
index 50c77163..b14fd482 100644
--- a/contrib/30.readline/src/readline.c
+++ b/contrib/30.readline/src/readline.c
@@ -19,7 +19,7 @@ pic_rl_readline(pic_state *pic)
   result = readline(prompt);
 
   if(result)
-    return pic_obj_value(pic_make_cstr(pic, result));
+    return pic_obj_value(pic_cstr_value(pic, result));
   else
     return pic_eof_object(pic);
 }
@@ -87,7 +87,7 @@ pic_rl_current_history(pic_state *pic)
 {
   pic_get_args(pic, "");
 
-  return pic_obj_value(pic_make_cstr(pic, current_history()->line));
+  return pic_obj_value(pic_cstr_value(pic, current_history()->line));
 }
 
 static pic_value
@@ -100,7 +100,7 @@ pic_rl_history_get(pic_state *pic)
   
   e = history_get(i);
 
-  return e ? pic_obj_value(pic_make_cstr(pic, e->line))
+  return e ? pic_obj_value(pic_cstr_value(pic, e->line))
     : pic_false_value(pic);
 }
 
@@ -114,7 +114,7 @@ pic_rl_remove_history(pic_state *pic)
   
   e = remove_history(i);
 
-  return e ? pic_obj_value(pic_make_cstr(pic, e->line))
+  return e ? pic_obj_value(pic_cstr_value(pic, e->line))
     : pic_false_value(pic);
 }
 
@@ -148,7 +148,7 @@ pic_rl_previous_history(pic_state *pic)
 
   e = previous_history();
 
-  return e ? pic_obj_value(pic_make_cstr(pic, e->line))
+  return e ? pic_obj_value(pic_cstr_value(pic, e->line))
     : pic_false_value(pic);
 }
 
@@ -161,7 +161,7 @@ pic_rl_next_history(pic_state *pic)
 
   e = next_history();
 
-  return e ? pic_obj_value(pic_make_cstr(pic, e->line))
+  return e ? pic_obj_value(pic_cstr_value(pic, e->line))
     : pic_false_value(pic);
 }
 
@@ -240,7 +240,7 @@ pic_rl_history_expand(pic_state *pic)
   if(status == -1 || status == 2)
     pic_errorf(pic, "%s\n", result);
 
-  return pic_obj_value(pic_make_cstr(pic, result));
+  return pic_obj_value(pic_cstr_value(pic, result));
 }
 
 void
diff --git a/contrib/30.regexp/src/regexp.c b/contrib/30.regexp/src/regexp.c
index 64740f8a..1a4ad678 100644
--- a/contrib/30.regexp/src/regexp.c
+++ b/contrib/30.regexp/src/regexp.c
@@ -62,7 +62,7 @@ pic_regexp_regexp(pic_state *pic)
     pic_errorf(pic, "regexp compilation error: %s", errbuf);
   }
 
-  return pic_obj_value(pic_data_alloc(pic, &regexp_type, reg));
+  return pic_obj_value(pic_data_value(pic, reg, &regexp_type));
 }
 
 static pic_value
@@ -97,7 +97,7 @@ pic_regexp_regexp_match(pic_state *pic)
 
     offset = 0;
     while (regexec(&pic_regexp_data_ptr(reg)->reg, input, 1, match, 0) != REG_NOMATCH) {
-      pic_push(pic, pic_obj_value(pic_make_str(pic, input, match[0].rm_eo - match[0].rm_so)), matches);
+      pic_push(pic, pic_obj_value(pic_str_value(pic, input, match[0].rm_eo - match[0].rm_so)), matches);
       pic_push(pic, pic_int_value(pic, offset), positions);
 
       offset += match[0].rm_eo;
@@ -111,7 +111,7 @@ pic_regexp_regexp_match(pic_state *pic)
         if (match[i].rm_so == -1) {
           break;
         }
-        str = pic_make_str(pic, input + match[i].rm_so, match[i].rm_eo - match[i].rm_so);
+        str = pic_str_value(pic, input + match[i].rm_so, match[i].rm_eo - match[i].rm_so);
         pic_push(pic, pic_obj_value(str), matches);
         pic_push(pic, pic_int_value(pic, match[i].rm_so), positions);
       }
@@ -141,12 +141,12 @@ pic_regexp_regexp_split(pic_state *pic)
   pic_assert_type(pic, reg, regexp);
 
   while (regexec(&pic_regexp_data_ptr(reg)->reg, input, 1, &match, 0) != REG_NOMATCH) {
-    pic_push(pic, pic_obj_value(pic_make_str(pic, input, match.rm_so)), output);
+    pic_push(pic, pic_obj_value(pic_str_value(pic, input, match.rm_so)), output);
 
     input += match.rm_eo;
   }
 
-  pic_push(pic, pic_obj_value(pic_make_cstr(pic, input)), output);
+  pic_push(pic, pic_obj_value(pic_cstr_value(pic, input)), output);
 
   return pic_reverse(pic, output);
 }
@@ -157,20 +157,20 @@ pic_regexp_regexp_replace(pic_state *pic)
   pic_value reg;
   const char *input;
   regmatch_t match;
-  struct pic_string *txt, *output = pic_make_lit(pic, "");
+  struct pic_string *txt, *output = pic_lit_value(pic, "");
 
   pic_get_args(pic, "ozs", &reg, &input, &txt);
 
   pic_assert_type(pic, reg, regexp);
 
   while (regexec(&pic_regexp_data_ptr(reg)->reg, input, 1, &match, 0) != REG_NOMATCH) {
-    output = pic_str_cat(pic, output, pic_make_str(pic, input, match.rm_so));
+    output = pic_str_cat(pic, output, pic_str_value(pic, input, match.rm_so));
     output = pic_str_cat(pic, output, txt);
 
     input += match.rm_eo;
   }
 
-  output = pic_str_cat(pic, output, pic_make_str(pic, input, strlen(input)));
+  output = pic_str_cat(pic, output, pic_str_value(pic, input, strlen(input)));
 
   return pic_obj_value(output);
 }
diff --git a/contrib/40.srfi/src/106.c b/contrib/40.srfi/src/106.c
index f88504de..fcd4e6f9 100644
--- a/contrib/40.srfi/src/106.c
+++ b/contrib/40.srfi/src/106.c
@@ -80,10 +80,10 @@ pic_socket_make_socket(pic_state *pic)
 
   node = service = NULL;
   if (pic_str_p(pic, n)) {
-    node = pic_str_cstr(pic, pic_str_ptr(n));
+    node = pic_str(pic, pic_str_ptr(n));
   }
   if (pic_str_p(pic, s)) {
-    service = pic_str_cstr(pic, pic_str_ptr(s));
+    service = pic_str(pic, pic_str_ptr(s));
   }
 
   sock = pic_malloc(pic, sizeof(struct pic_socket_t));
@@ -147,7 +147,7 @@ pic_socket_make_socket(pic_state *pic)
     pic_errorf(pic, "%s", strerror(errno));
   }
 
-  return pic_obj_value(pic_data_alloc(pic, &socket_type, sock));
+  return pic_obj_value(pic_data_value(pic, sock, &socket_type));
 }
 
 static pic_value
@@ -185,7 +185,7 @@ pic_socket_socket_accept(pic_state *pic)
 
   new_sock = pic_malloc(pic, sizeof(struct pic_socket_t));
   new_sock->fd = fd;
-  return pic_obj_value(pic_data_alloc(pic, &socket_type, new_sock));
+  return pic_obj_value(pic_data_value(pic, new_sock, &socket_type));
 }
 
 static pic_value
diff --git a/docs/capi.rst b/docs/capi.rst
index c427515e..6e701fb9 100644
--- a/docs/capi.rst
+++ b/docs/capi.rst
@@ -89,7 +89,7 @@ When you use dynamic memory allocation inside C APIs, you must be caseful about
 
     f = create_foo();
 
-    data = pic_data_alloc(pic, &foo_type, md);
+    data = pic_data_value(pic, md, &foo_type);
 
     return pic_obj_value(data);
   }
diff --git a/extlib/benz/cont.c b/extlib/benz/cont.c
index 8dac1bcd..80ce6c54 100644
--- a/extlib/benz/cont.c
+++ b/extlib/benz/cont.c
@@ -124,7 +124,7 @@ pic_make_cont(pic_state *pic, struct pic_cont *cont)
   struct pic_proc *c;
 
   /* save the escape continuation in proc */
-  c = pic_lambda(pic, cont_call, 2, pic_int_value(pic, cont->id), pic_obj_value(pic_data_alloc(pic, &cont_type, cont)));
+  c = pic_lambda(pic, cont_call, 2, pic_int_value(pic, cont->id), pic_obj_value(pic_data_value(pic, cont, &cont_type)));
 
   return c;
 }
diff --git a/extlib/benz/data.c b/extlib/benz/data.c
index a570b6be..e2402a2d 100644
--- a/extlib/benz/data.c
+++ b/extlib/benz/data.c
@@ -1,13 +1,2 @@
 #include "picrin.h"
 
-struct pic_data *
-pic_data_alloc(pic_state *pic, const pic_data_type *type, void *userdata)
-{
-  struct pic_data *data;
-
-  data = (struct pic_data *)pic_obj_alloc(pic, sizeof(struct pic_data), PIC_TYPE_DATA);
-  data->type = type;
-  data->data = userdata;
-
-  return data;
-}
diff --git a/extlib/benz/debug.c b/extlib/benz/debug.c
index 6ef57678..7bde1990 100644
--- a/extlib/benz/debug.c
+++ b/extlib/benz/debug.c
@@ -11,18 +11,18 @@ pic_get_backtrace(pic_state *pic)
   pic_callinfo *ci;
   struct pic_string *trace;
 
-  trace = pic_make_lit(pic, "");
+  trace = pic_lit_value(pic, "");
 
   for (ci = pic->ci; ci != pic->cibase; --ci) {
     struct pic_proc *proc = pic_proc_ptr(ci->fp[0]);
 
-    trace = pic_str_cat(pic, trace, pic_make_lit(pic, "  at "));
-    trace = pic_str_cat(pic, trace, pic_make_lit(pic, "(anonymous lambda)"));
+    trace = pic_str_cat(pic, trace, pic_lit_value(pic, "  at "));
+    trace = pic_str_cat(pic, trace, pic_lit_value(pic, "(anonymous lambda)"));
 
     if (pic_proc_func_p(proc)) {
-      trace = pic_str_cat(pic, trace, pic_make_lit(pic, " (native function)\n"));
+      trace = pic_str_cat(pic, trace, pic_lit_value(pic, " (native function)\n"));
     } else if (pic_proc_irep_p(proc)) {
-      trace = pic_str_cat(pic, trace, pic_make_lit(pic, " (unknown location)\n")); /* TODO */
+      trace = pic_str_cat(pic, trace, pic_lit_value(pic, " (unknown location)\n")); /* TODO */
     }
   }
 
@@ -58,6 +58,6 @@ pic_print_backtrace(pic_state *pic, xFILE *file)
     }
     xfprintf(pic, file, "\n");
 
-    xfputs(pic, pic_str_cstr(pic, e->stack), file);
+    xfputs(pic, pic_str(pic, e->stack), file);
   }
 }
diff --git a/extlib/benz/error.c b/extlib/benz/error.c
index b416ed18..39c2e9d9 100644
--- a/extlib/benz/error.c
+++ b/extlib/benz/error.c
@@ -24,10 +24,10 @@ pic_warnf(pic_state *pic, const char *fmt, ...)
   struct pic_string *err;
 
   va_start(ap, fmt);
-  err = pic_vformat(pic, fmt, ap);
+  err = pic_vstrf_value(pic, fmt, ap);
   va_end(ap);
 
-  xfprintf(pic, pic_stderr(pic)->file, "warn: %s\n", pic_str_cstr(pic, err));
+  xfprintf(pic, pic_stderr(pic)->file, "warn: %s\n", pic_str(pic, err));
 }
 
 void
@@ -38,10 +38,10 @@ pic_errorf(pic_state *pic, const char *fmt, ...)
   struct pic_string *err;
 
   va_start(ap, fmt);
-  err = pic_vformat(pic, fmt, ap);
+  err = pic_vstrf_value(pic, fmt, ap);
   va_end(ap);
 
-  msg = pic_str_cstr(pic, err);
+  msg = pic_str(pic, err);
 
   pic_error(pic, msg, pic_nil_value(pic));
 }
@@ -100,7 +100,7 @@ pic_make_error(pic_state *pic, pic_sym *type, const char *msg, pic_value irrs)
 
   e = (struct pic_error *)pic_obj_alloc(pic, sizeof(struct pic_error), PIC_TYPE_ERROR);
   e->type = type;
-  e->msg = pic_make_cstr(pic, msg);
+  e->msg = pic_cstr_value(pic, msg);
   e->irrs = irrs;
   e->stack = stack;
 
diff --git a/extlib/benz/gc.c b/extlib/benz/gc.c
index e0c53e81..0e4ef903 100644
--- a/extlib/benz/gc.c
+++ b/extlib/benz/gc.c
@@ -702,7 +702,7 @@ pic_alloca(pic_state *pic, size_t n)
   static const pic_data_type t = { "pic_alloca", pic_free, 0 };
 
   /* TODO: optimize */
-  return pic_data_alloc(pic, &t, pic_malloc(pic, n))->data;
+  return pic_data_value(pic, pic_malloc(pic, n), &t)->data;
 }
 
 struct pic_object *
diff --git a/extlib/benz/include/picrin.h b/extlib/benz/include/picrin.h
index 6515bac7..7744f27b 100644
--- a/extlib/benz/include/picrin.h
+++ b/extlib/benz/include/picrin.h
@@ -61,6 +61,7 @@ struct pic_proc;
 struct pic_port;
 struct pic_error;
 struct pic_env;
+struct pic_data;
 
 typedef struct pic_symbol pic_sym;
 typedef struct pic_id pic_id;
@@ -165,6 +166,20 @@ pic_value pic_applyk(pic_state *, struct pic_proc *proc, int n, pic_value *argv)
 #define pic_port_p(pic, v) (pic_type(pic, v) == PIC_TYPE_PORT)
 #define pic_sym_p(pic,v) (pic_type(pic,v) == PIC_TYPE_SYMBOL)
 
+int pic_int(pic_state *, pic_value);
+double pic_float(pic_state *, pic_value);
+char pic_char(pic_state *, pic_value);
+bool pic_bool(pic_state *, pic_value);
+const char *pic_str(pic_state *, struct pic_string *);
+unsigned char *pic_blob(pic_state *, struct pic_blob *, int *len);
+void *pic_data(pic_state *, struct pic_data *);
+
+typedef struct {
+  const char *type_name;
+  void (*dtor)(pic_state *, void *);
+  void (*mark)(pic_state *, void *, void (*)(pic_state *, pic_value));
+} pic_data_type;
+
 pic_value pic_undef_value(pic_state *);
 pic_value pic_int_value(pic_state *, int);
 pic_value pic_float_value(pic_state *, double);
@@ -173,14 +188,13 @@ pic_value pic_true_value(pic_state *);
 pic_value pic_false_value(pic_state *);
 pic_value pic_bool_value(pic_state *, bool);
 pic_value pic_eof_object(pic_state *);
-
-int pic_int(pic_state *, pic_value);
-double pic_float(pic_state *, pic_value);
-char pic_char(pic_state *, pic_value);
-bool pic_bool(pic_state *, pic_value);
-/* const char *pic_str(pic_state *, pic_value); */
-/* unsigned char *pic_blob(pic_state *, pic_value, int *len); */
-/* void *pic_data(pic_state *, pic_value); */
+struct pic_string *pic_str_value(pic_state *, const char *str, int len);
+#define pic_cstr_value(pic, cstr) pic_str_value(pic, (cstr), strlen(cstr))
+#define pic_lit_value(pic, lit) pic_str_value(pic, "" lit, -((int)sizeof lit - 1))
+struct pic_string *pic_strf_value(pic_state *, const char *fmt, ...);
+struct pic_string *pic_vstrf_value(pic_state *, const char *fmt, va_list ap);
+struct pic_blob *pic_blob_value(pic_state *, const unsigned char *buf, int len);
+struct pic_data *pic_data_value(pic_state *, void *ptr, const pic_data_type *type);
 
 int pic_type(pic_state *, pic_value);
 const char *pic_typename(pic_state *, int);
@@ -227,10 +241,10 @@ bool pic_weak_has(pic_state *, struct pic_weak *, void *);
 
 /* symbol */
 pic_sym *pic_intern(pic_state *, struct pic_string *);
-#define pic_intern_str(pic,s,i) pic_intern(pic, pic_make_str(pic, (s), (i)))
-#define pic_intern_cstr(pic,s) pic_intern(pic, pic_make_cstr(pic, (s)))
-#define pic_intern_lit(pic,lit) pic_intern(pic, pic_make_lit(pic, lit))
-const char *pic_symbol_name(pic_state *, pic_sym *);
+#define pic_intern_str(pic,s,i) pic_intern(pic, pic_str_value(pic, (s), (i)))
+#define pic_intern_cstr(pic,s) pic_intern(pic, pic_cstr_value(pic, (s)))
+#define pic_intern_lit(pic,lit) pic_intern(pic, pic_lit_value(pic, lit))
+struct pic_string *pic_sym_name(pic_state *, pic_sym *);
 
 /* string */
 int pic_str_len(pic_state *, struct pic_string *);
diff --git a/extlib/benz/include/picrin/data.h b/extlib/benz/include/picrin/data.h
index 6a701faa..60fe6dc2 100644
--- a/extlib/benz/include/picrin/data.h
+++ b/extlib/benz/include/picrin/data.h
@@ -9,12 +9,6 @@
 extern "C" {
 #endif
 
-typedef struct {
-  const char *type_name;
-  void (*dtor)(pic_state *, void *);
-  void (*mark)(pic_state *, void *, void (*)(pic_state *, pic_value));
-} pic_data_type;
-
 struct pic_data {
   PIC_OBJECT_HEADER
   const pic_data_type *type;
@@ -27,8 +21,6 @@ PIC_INLINE bool pic_data_type_p(pic_state *pic, const pic_value obj, const pic_d
   return pic_data_p(pic, obj) && pic_data_ptr(obj)->type == type;
 }
 
-struct pic_data *pic_data_alloc(pic_state *, const pic_data_type *, void *);
-
 #if defined(__cplusplus)
 }
 #endif
diff --git a/extlib/benz/include/picrin/string.h b/extlib/benz/include/picrin/string.h
index 117fc24e..7d4eeab0 100644
--- a/extlib/benz/include/picrin/string.h
+++ b/extlib/benz/include/picrin/string.h
@@ -19,15 +19,6 @@ void pic_rope_decref(pic_state *, struct pic_rope *);
 
 #define pic_str_ptr(o) ((struct pic_string *)pic_obj_ptr(o))
 
-struct pic_string *pic_make_str(pic_state *, const char *, int);
-#define pic_make_cstr(pic, cstr) pic_make_str(pic, (cstr), strlen(cstr))
-#define pic_make_lit(pic, lit) pic_make_str(pic, "" lit, -((int)sizeof lit - 1))
-
-const char *pic_str_cstr(pic_state *, struct pic_string *);
-
-struct pic_string *pic_format(pic_state *, const char *, ...);
-struct pic_string *pic_vformat(pic_state *, const char *, va_list);
-
 #if defined(__cplusplus)
 }
 #endif
diff --git a/extlib/benz/lib.c b/extlib/benz/lib.c
index d47051f5..311f6ed5 100644
--- a/extlib/benz/lib.c
+++ b/extlib/benz/lib.c
@@ -61,11 +61,11 @@ pic_make_library(pic_state *pic, const char *lib)
     old_lib = pic_current_library(pic);
   }
 
-  name = pic_make_cstr(pic, lib);
+  name = pic_cstr_value(pic, lib);
   env = make_library_env(pic, name);
   exports = pic_make_dict(pic);
 
-  it = kh_put(ltable, h, pic_str_cstr(pic, name), &ret);
+  it = kh_put(ltable, h, pic_str(pic, name), &ret);
   if (ret == 0) {               /* if exists */
     pic_errorf(pic, "library name already in use: %s", lib);
   }
@@ -94,7 +94,7 @@ pic_find_library(pic_state *pic, const char *lib)
 const char *
 pic_current_library(pic_state *pic)
 {
-  return pic_str_cstr(pic, pic->lib->name);
+  return pic_str(pic, pic->lib->name);
 }
 
 struct pic_env *
diff --git a/extlib/benz/macro.c b/extlib/benz/macro.c
index 1df08a07..8a65f594 100644
--- a/extlib/benz/macro.c
+++ b/extlib/benz/macro.c
@@ -42,9 +42,9 @@ pic_add_identifier(pic_state *pic, pic_id *id, struct pic_env *env)
   name = pic_identifier_name(pic, id);
 
   if (env->up == NULL && pic_sym_p(pic, pic_obj_value(id))) { /* toplevel & public */
-    str = pic_format(pic, "%s/%s", pic_str_cstr(pic, env->lib), name);
+    str = pic_strf_value(pic, "%s/%s", pic_str(pic, env->lib), name);
   } else {
-    str = pic_format(pic, ".%s.%d", name, pic->ucnt++);
+    str = pic_strf_value(pic, ".%s.%d", name, pic->ucnt++);
   }
   uid = pic_intern(pic, str);
 
diff --git a/extlib/benz/number.c b/extlib/benz/number.c
index 580e481e..423c8287 100644
--- a/extlib/benz/number.c
+++ b/extlib/benz/number.c
@@ -234,7 +234,7 @@ pic_number_number_to_string(pic_state *pic)
 
     number_string(ival, radix, ilen, buf);
 
-    str = pic_make_str(pic, buf, s - 1);
+    str = pic_str_value(pic, buf, s - 1);
 
     pic_free(pic, buf);
   }
diff --git a/extlib/benz/port.c b/extlib/benz/port.c
index 4ad2251c..5647f76f 100644
--- a/extlib/benz/port.c
+++ b/extlib/benz/port.c
@@ -108,7 +108,7 @@ pic_open_file(pic_state *pic, const char *name, int flags) {
     mode = 'w';
   }
   if ((file = file_open(pic, name, &mode)) == NULL) {
-    file_error(pic, pic_str_cstr(pic, pic_format(pic, "could not open file '%s'", name)));
+    file_error(pic, pic_str(pic, pic_strf_value(pic, "could not open file '%s'", name)));
   }
 
   port = (struct pic_port *)pic_obj_alloc(pic, sizeof(struct pic_port), PIC_TYPE_PORT);
@@ -298,7 +298,7 @@ pic_get_output_string(pic_state *pic, struct pic_port *port)
 
   s = port->file->vtable.cookie;
 
-  return pic_make_str(pic, s->buf, s->end);
+  return pic_str_value(pic, s->buf, s->end);
 }
 
 void
diff --git a/extlib/benz/proc.c b/extlib/benz/proc.c
index 0430c661..c77c9a9a 100644
--- a/extlib/benz/proc.c
+++ b/extlib/benz/proc.c
@@ -141,7 +141,7 @@ pic_get_args(pic_state *pic, const char *format, ...)
       }
 
     VAL_CASE('c', char, char, pic_char(pic, v))
-    VAL_CASE('z', str, const char *, pic_str_cstr(pic, pic_str_ptr(v)))
+    VAL_CASE('z', str, const char *, pic_str(pic, pic_str_ptr(v)))
 
 #define PTR_CASE(c, type, ctype)                        \
       VAL_CASE(c, type, ctype, pic_## type ##_ptr(v))
@@ -179,7 +179,7 @@ static pic_value
 vm_gref(pic_state *pic, pic_sym *uid)
 {
   if (! pic_weak_has(pic, pic->globals, uid)) {
-    pic_errorf(pic, "uninitialized global variable: %s", pic_symbol_name(pic, uid));
+    pic_errorf(pic, "uninitialized global variable: %s", pic_str(pic, pic_sym_name(pic, uid)));
   }
   return pic_weak_ref(pic, pic->globals, uid);
 }
@@ -308,12 +308,12 @@ pic_vm_tear_off(pic_state *pic)
     puts(")");                                                          \
     if (! pic_proc_func_p(proc)) {                                      \
       printf("  irep = %p\n", proc->u.i.irep);                          \
-      printf("  name = %s\n", pic_symbol_name(pic, pic_proc_name(proc))); \
+      printf("  name = %s\n", pic_str(pic, pic_sym_name(pic, pic_proc_name(proc)))); \
       pic_dump_irep(proc->u.i.irep);                                    \
     }                                                                   \
     else {                                                              \
       printf("  cfunc = %p\n", (void *)proc->u.f.func);                 \
-      printf("  name = %s\n", pic_symbol_name(pic, pic_proc_name(proc))); \
+      printf("  name = %s\n", pic_str(pic, pic_sym_name(pic, pic_proc_name(proc)))); \
     }                                                                   \
     puts("== end\n");                                                   \
   } while (0)
diff --git a/extlib/benz/read.c b/extlib/benz/read.c
index 59aee417..c4982a0b 100644
--- a/extlib/benz/read.c
+++ b/extlib/benz/read.c
@@ -282,7 +282,7 @@ read_unsigned(pic_state *pic, struct pic_port *port, int c)
   }
   if (idx >= ATOF_BUF_SIZE)
     read_error(pic, "number too large", 
-                    pic_obj_value(pic_make_str(pic, (const char *)buf, ATOF_BUF_SIZE)));
+                    pic_obj_value(pic_str_value(pic, (const char *)buf, ATOF_BUF_SIZE)));
 
   if (! isdelim(c))
     read_error(pic, "non-delimiter character given after number", pic_list1(pic, pic_char_value(pic, c)));
@@ -321,10 +321,10 @@ read_minus(pic_state *pic, struct pic_port *port, int c)
   }
   else {
     sym = read_symbol(pic, port, c);
-    if (strcaseeq(pic_symbol_name(pic, pic_sym_ptr(sym)), "-inf.0")) {
+    if (strcaseeq(pic_str(pic, pic_sym_name(pic, pic_sym_ptr(sym))), "-inf.0")) {
       return pic_float_value(pic, -(1.0 / 0.0));
     }
-    if (strcaseeq(pic_symbol_name(pic, pic_sym_ptr(sym)), "-nan.0")) {
+    if (strcaseeq(pic_str(pic, pic_sym_name(pic, pic_sym_ptr(sym))), "-nan.0")) {
       return pic_float_value(pic, -(0.0 / 0.0));
     }
     return sym;
@@ -341,10 +341,10 @@ read_plus(pic_state *pic, struct pic_port *port, int c)
   }
   else {
     sym = read_symbol(pic, port, c);
-    if (strcaseeq(pic_symbol_name(pic, pic_sym_ptr(sym)), "+inf.0")) {
+    if (strcaseeq(pic_str(pic, pic_sym_name(pic, pic_sym_ptr(sym))), "+inf.0")) {
       return pic_float_value(pic, 1.0 / 0.0);
     }
-    if (strcaseeq(pic_symbol_name(pic, pic_sym_ptr(sym)), "+nan.0")) {
+    if (strcaseeq(pic_str(pic, pic_sym_name(pic, pic_sym_ptr(sym))), "+nan.0")) {
       return pic_float_value(pic, 0.0 / 0.0);
     }
     return sym;
@@ -444,7 +444,7 @@ read_string(pic_state *pic, struct pic_port *port, int c)
   }
   buf[cnt] = '\0';
 
-  str = pic_make_str(pic, buf, cnt);
+  str = pic_str_value(pic, buf, cnt);
   pic_free(pic, buf);
   return pic_obj_value(str);
 }
diff --git a/extlib/benz/string.c b/extlib/benz/string.c
index e29ffb32..90103455 100644
--- a/extlib/benz/string.c
+++ b/extlib/benz/string.c
@@ -94,7 +94,7 @@ pic_make_rope(pic_state *pic, struct pic_chunk *c)
 }
 
 static struct pic_string *
-pic_make_string(pic_state *pic, struct pic_rope *rope)
+pic_str_valueing(pic_state *pic, struct pic_rope *rope)
 {
   struct pic_string *str;
 
@@ -237,7 +237,7 @@ rope_cstr(pic_state *pic, struct pic_rope *x)
 }
 
 struct pic_string *
-pic_make_str(pic_state *pic, const char *str, int len)
+pic_str_value(pic_state *pic, const char *str, int len)
 {
   struct pic_chunk *c;
 
@@ -249,7 +249,7 @@ pic_make_str(pic_state *pic, const char *str, int len)
     }
     c = pic_make_chunk_lit(pic, str, -len);
   }
-  return pic_make_string(pic, pic_make_rope(pic, c));
+  return pic_str_valueing(pic, pic_make_rope(pic, c));
 }
 
 int
@@ -273,19 +273,19 @@ pic_str_ref(pic_state *pic, struct pic_string *str, int i)
 struct pic_string *
 pic_str_cat(pic_state *pic, struct pic_string *a, struct pic_string *b)
 {
-  return pic_make_string(pic, rope_cat(pic, a->rope, b->rope));
+  return pic_str_valueing(pic, rope_cat(pic, a->rope, b->rope));
 }
 
 struct pic_string *
 pic_str_sub(pic_state *pic, struct pic_string *str, int s, int e)
 {
-  return pic_make_string(pic, rope_sub(pic, str->rope, s, e));
+  return pic_str_valueing(pic, rope_sub(pic, str->rope, s, e));
 }
 
 int
 pic_str_cmp(pic_state *pic, struct pic_string *str1, struct pic_string *str2)
 {
-  return strcmp(pic_str_cstr(pic, str1), pic_str_cstr(pic, str2));
+  return strcmp(pic_str(pic, str1), pic_str(pic, str2));
 }
 
 int
@@ -294,7 +294,7 @@ pic_str_hash(pic_state *pic, struct pic_string *str)
   const char *s;
   int h = 0;
 
-  s = pic_str_cstr(pic, str);
+  s = pic_str(pic, str);
   while (*s) {
     h = (h << 5) - h + *s++;
   }
@@ -302,7 +302,7 @@ pic_str_hash(pic_state *pic, struct pic_string *str)
 }
 
 const char *
-pic_str_cstr(pic_state *pic, struct pic_string *str)
+pic_str(pic_state *pic, struct pic_string *str)
 {
   return rope_cstr(pic, str->rope);
 }
@@ -374,7 +374,7 @@ pic_vfformat(pic_state *pic, xFILE *file, const char *fmt, va_list ap)
 }
 
 struct pic_string *
-pic_vformat(pic_state *pic, const char *fmt, va_list ap)
+pic_vstrf_value(pic_state *pic, const char *fmt, va_list ap)
 {
   struct pic_port *port;
   struct pic_string *str;
@@ -389,13 +389,13 @@ pic_vformat(pic_state *pic, const char *fmt, va_list ap)
 }
 
 struct pic_string *
-pic_format(pic_state *pic, const char *fmt, ...)
+pic_strf_value(pic_state *pic, const char *fmt, ...)
 {
   va_list ap;
   struct pic_string *str;
 
   va_start(ap, fmt);
-  str = pic_vformat(pic, fmt, ap);
+  str = pic_vstrf_value(pic, fmt, ap);
   va_end(ap);
 
   return str;
@@ -428,7 +428,7 @@ pic_str_string(pic_state *pic)
     buf[i] = pic_char(pic, argv[i]);
   }
 
-  str = pic_make_str(pic, buf, argc);
+  str = pic_str_value(pic, buf, argc);
   pic_free(pic, buf);
 
   return pic_obj_value(str);
@@ -447,7 +447,7 @@ pic_str_make_string(pic_state *pic)
   buf = pic_malloc(pic, len);
   memset(buf, c, len);
 
-  ret = pic_obj_value(pic_make_str(pic, buf, len));
+  ret = pic_obj_value(pic_str_value(pic, buf, len));
 
   pic_free(pic, buf);
   return ret;
@@ -536,7 +536,7 @@ pic_str_string_append(pic_state *pic)
 
   pic_get_args(pic, "*", &argc, &argv);
 
-  str = pic_make_lit(pic, "");
+  str = pic_lit_value(pic, "");
   for (i = 0; i < argc; ++i) {
     if (! pic_str_p(pic, argv[i])) {
       pic_errorf(pic, "type error");
@@ -583,7 +583,7 @@ pic_str_string_map(pic_state *pic)
       pic_assert_type(pic, val, char);
       buf[i] = pic_char(pic, val);
     }
-    str = pic_make_str(pic, buf, len);
+    str = pic_str_value(pic, buf, len);
   }
   pic_catch {
     pic_free(pic, buf);
@@ -640,7 +640,7 @@ pic_str_list_to_string(pic_state *pic)
   pic_get_args(pic, "o", &list);
 
   if (pic_length(pic, list) == 0) {
-    return pic_obj_value(pic_make_lit(pic, ""));
+    return pic_obj_value(pic_lit_value(pic, ""));
   }
 
   buf = pic_malloc(pic, pic_length(pic, list));
@@ -653,7 +653,7 @@ pic_str_list_to_string(pic_state *pic)
       buf[i++] = pic_char(pic, e);
     }
 
-    str = pic_make_str(pic, buf, i);
+    str = pic_str_value(pic, buf, i);
   }
   pic_catch {
     pic_free(pic, buf);
diff --git a/extlib/benz/symbol.c b/extlib/benz/symbol.c
index 51e9cfbc..c1cc75cc 100644
--- a/extlib/benz/symbol.c
+++ b/extlib/benz/symbol.c
@@ -44,10 +44,10 @@ pic_make_identifier(pic_state *pic, pic_id *id, struct pic_env *env)
   return nid;
 }
 
-const char *
-pic_symbol_name(pic_state *pic, pic_sym *sym)
+struct pic_string *
+pic_sym_name(pic_state PIC_UNUSED(*pic), pic_sym *sym)
 {
-  return pic_str_cstr(pic, sym->str);
+  return sym->str;
 }
 
 const char *
@@ -57,7 +57,7 @@ pic_identifier_name(pic_state *pic, pic_id *id)
     id = id->u.id.id;
   }
 
-  return pic_symbol_name(pic, (pic_sym *)id);
+  return pic_str(pic, pic_sym_name(pic, (pic_sym *)id));
 }
 
 static pic_value
diff --git a/extlib/benz/value.c b/extlib/benz/value.c
index e0857dfb..b0339702 100644
--- a/extlib/benz/value.c
+++ b/extlib/benz/value.c
@@ -72,3 +72,21 @@ pic_typename(pic_state *pic, int type)
     pic_errorf(pic, "pic_typename: invalid type given %d", type);
   }
 }
+
+void *
+pic_data(pic_state PIC_UNUSED(*pic), struct pic_data *data)
+{
+  return data->data;
+}
+
+struct pic_data *
+pic_data_value(pic_state *pic, void *userdata, const pic_data_type *type)
+{
+  struct pic_data *data;
+
+  data = (struct pic_data *)pic_obj_alloc(pic, sizeof(struct pic_data), PIC_TYPE_DATA);
+  data->type = type;
+  data->data = userdata;
+
+  return data;
+}
diff --git a/extlib/benz/vector.c b/extlib/benz/vector.c
index 1aa87e76..358ad54e 100644
--- a/extlib/benz/vector.c
+++ b/extlib/benz/vector.c
@@ -346,7 +346,7 @@ pic_vec_vector_to_string(pic_state *pic)
     buf[i - start] = pic_char(pic, vec->data[i]);
   }
 
-  str = pic_make_str(pic, buf, end - start);
+  str = pic_str_value(pic, buf, end - start);
   pic_free(pic, buf);
 
   return pic_obj_value(str);
diff --git a/extlib/benz/write.c b/extlib/benz/write.c
index 426f9804..73bba09e 100644
--- a/extlib/benz/write.c
+++ b/extlib/benz/write.c
@@ -85,10 +85,10 @@ static void
 write_str(pic_state *pic, struct pic_string *str, xFILE *file, int mode)
 {
   int i;
-  const char *cstr = pic_str_cstr(pic, str);
+  const char *cstr = pic_str(pic, str);
 
   if (mode == DISPLAY_MODE) {
-    xfprintf(pic, file, "%s", pic_str_cstr(pic, str));
+    xfprintf(pic, file, "%s", pic_str(pic, str));
     return;
   }
   xfprintf(pic, file, "\"");
@@ -246,7 +246,7 @@ write_dict(struct writer_control *p, struct pic_dict *dict)
 
   xfprintf(pic, file, "#.(dictionary");
   pic_dict_for_each (sym, dict, it) {
-    xfprintf(pic, file, " '%s ", pic_symbol_name(pic, sym));
+    xfprintf(pic, file, " '%s ", pic_str(pic, pic_sym_name(pic, sym)));
     write_core(p, pic_dict_ref(pic, dict, sym));
   }
   xfprintf(pic, file, ")");
@@ -298,7 +298,7 @@ write_core(struct writer_control *p, pic_value obj)
     write_float(pic, pic_float(pic, obj), file);
     break;
   case PIC_TYPE_SYMBOL:
-    xfprintf(pic, file, "%s", pic_symbol_name(pic, pic_sym_ptr(obj)));
+    xfprintf(pic, file, "%s", pic_str(pic, pic_sym_name(pic, pic_sym_ptr(obj))));
     break;
   case PIC_TYPE_BLOB:
     write_blob(pic, pic_blob_ptr(obj), file);
@@ -440,11 +440,11 @@ pic_printf(pic_state *pic, const char *fmt, ...)
 
   va_start(ap, fmt);
 
-  str = pic_vformat(pic, fmt, ap);
+  str = pic_vstrf_value(pic, fmt, ap);
 
   va_end(ap);
 
-  xfprintf(pic, file, "%s", pic_str_cstr(pic, str));
+  xfprintf(pic, file, "%s", pic_str(pic, str));
   xfflush(pic, file);
 }