diff --git a/contrib/20.r7rs/src/load.c b/contrib/20.r7rs/src/load.c
index 3503eda9..f6f68b63 100644
--- a/contrib/20.r7rs/src/load.c
+++ b/contrib/20.r7rs/src/load.c
@@ -18,7 +18,7 @@ pic_load_load(pic_state *pic)
 
   fp = fopen(fn, "r");
   if (fp == NULL) {
-    pic_errorf(pic, "load: could not open file %s", fn);
+    pic_error(pic, "load: could not open file", 1, pic_cstr_value(pic, fn));
   }
 
   port = pic_open_port(pic, xfopen_file(pic, fp, "r"));
diff --git a/contrib/30.readline/src/readline.c b/contrib/30.readline/src/readline.c
index 6153cdbb..2a58b2c6 100644
--- a/contrib/30.readline/src/readline.c
+++ b/contrib/30.readline/src/readline.c
@@ -194,7 +194,7 @@ pic_rl_read_history(pic_state *pic)
   pic_get_args(pic, "z", &filename);
 
   if(read_history(filename))
-    pic_errorf(pic, "cannot read history file : %s", filename);
+    pic_error(pic, "cannot read history file", 1, pic_cstr_value(pic, filename));
   
   return pic_undef_value(pic);
 }
@@ -207,7 +207,7 @@ pic_rl_write_history(pic_state *pic)
   pic_get_args(pic, "z", &filename);
 
   if(write_history(filename))
-    pic_errorf(pic, "cannot write history file: %s", filename);
+    pic_error(pic, "cannot write history file", 1, pic_cstr_value(pic, filename));
   
   return pic_undef_value(pic);
 }
@@ -235,7 +235,7 @@ pic_rl_history_expand(pic_state *pic)
   
   status = history_expand(input,  &result);
   if(status == -1 || status == 2)
-    pic_errorf(pic, "%s\n", result);
+    pic_error(pic, result, 0);
 
   return pic_cstr_value(pic, result);
 }
diff --git a/contrib/30.regexp/src/regexp.c b/contrib/30.regexp/src/regexp.c
index 8f7f0c89..c428ad1c 100644
--- a/contrib/30.regexp/src/regexp.c
+++ b/contrib/30.regexp/src/regexp.c
@@ -57,7 +57,7 @@ pic_regexp_regexp(pic_state *pic)
     regerror(err, &reg->reg, errbuf, sizeof errbuf);
     regexp_dtor(pic, &reg->reg);
 
-    pic_errorf(pic, "regexp compilation error: %s", errbuf);
+    pic_error(pic, "regexp compilation error", 1, pic_cstr_value(pic, errbuf));
   }
 
   return pic_data_value(pic, reg, &regexp_type);
diff --git a/contrib/40.srfi/src/106.c b/contrib/40.srfi/src/106.c
index e2cdf13a..2ffec60a 100644
--- a/contrib/40.srfi/src/106.c
+++ b/contrib/40.srfi/src/106.c
@@ -31,7 +31,7 @@ PIC_INLINE void
 ensure_socket_is_open(pic_state *pic, struct pic_socket_t *sock)
 {
   if (sock != NULL && sock->fd == -1) {
-    pic_errorf(pic, "the socket is already closed");
+    pic_error(pic, "the socket is already closed", 0);
   }
 }
 
@@ -87,9 +87,9 @@ pic_socket_make_socket(pic_state *pic)
   } while (result == EAI_AGAIN);
   if (result) {
     if (result == EAI_SYSTEM) {
-      pic_errorf(pic, "%s", strerror(errno));
+      pic_error(pic, strerror(errno), 0);
     }
-    pic_errorf(pic, "%s", gai_strerror(result));
+    pic_error(pic, gai_strerror(result), 0);
   }
 
   for (it = ai; it != NULL; it = it->ai_next) {
@@ -129,7 +129,7 @@ pic_socket_make_socket(pic_state *pic)
   freeaddrinfo(ai);
 
   if (sock->fd == -1) {
-    pic_errorf(pic, "%s", strerror(errno));
+    pic_error(pic, strerror(errno), 0);
   }
 
   return pic_data_value(pic, sock, &socket_type);
@@ -158,7 +158,7 @@ pic_socket_socket_accept(pic_state *pic)
       } else if (errno == EAGAIN || errno == EWOULDBLOCK) {
         continue;
       } else {
-        pic_errorf(pic, "%s", strerror(errno));
+        pic_error(pic, strerror(errno), 0);
       }
     } else {
       break;
@@ -191,7 +191,7 @@ pic_socket_socket_send(pic_state *pic)
       } else if (errno == EAGAIN || errno == EWOULDBLOCK) {
         break;
       } else {
-        pic_errorf(pic, "%s", strerror(errno));
+        pic_error(pic, strerror(errno), 0);
       }
     }
     cursor += len;
@@ -214,7 +214,7 @@ pic_socket_socket_recv(pic_state *pic)
   pic_get_args(pic, "ui|i", &sock, &socket_type, &size, &flags);
 
   if (size < 0) {
-    pic_errorf(pic, "size must not be negative");
+    pic_error(pic, "size must not be negative", 0);
   }
 
   ensure_socket_is_open(pic, sock);
@@ -227,7 +227,7 @@ pic_socket_socket_recv(pic_state *pic)
   } while (len < 0 && (errno == EINTR || errno == EAGAIN || errno == EWOULDBLOCK));
 
   if (len < 0) {
-    pic_errorf(pic, "%s", strerror(errno));
+    pic_error(pic, strerror(errno), 0);
   }
 
   return pic_blob_value(pic, buf, len);
diff --git a/extlib/benz/blob.c b/extlib/benz/blob.c
index 3747d66e..bff9d67b 100644
--- a/extlib/benz/blob.c
+++ b/extlib/benz/blob.c
@@ -56,7 +56,7 @@ pic_blob_bytevector(pic_state *pic)
     pic_assert_type(pic, argv[i], int);
 
     if (pic_int(pic, argv[i]) < 0 || pic_int(pic, argv[i]) > 255) {
-      pic_errorf(pic, "byte out of range");
+      pic_error(pic, "byte out of range", 0);
     }
 
     *data++ = (unsigned char)pic_int(pic, argv[i]);
@@ -74,10 +74,10 @@ pic_blob_make_bytevector(pic_state *pic)
   pic_get_args(pic, "i|i", &k, &b);
 
   if (b < 0 || b > 255)
-    pic_errorf(pic, "byte out of range");
+    pic_error(pic, "byte out of range", 0);
 
   if (k < 0) {
-    pic_errorf(pic, "make-bytevector: negative length given %d", k);
+    pic_error(pic, "make-bytevector: negative length given", 1, pic_int_value(pic, k));
   }
 
   blob = pic_blob_value(pic, 0, k);
@@ -119,7 +119,7 @@ pic_blob_bytevector_u8_set(pic_state *pic)
   pic_get_args(pic, "bii", &buf, &len, &k, &v);
 
   if (v < 0 || v > 255)
-    pic_errorf(pic, "byte out of range");
+    pic_error(pic, "byte out of range", 0);
 
   VALID_INDEX(pic, len, k);
 
@@ -216,7 +216,7 @@ pic_blob_list_to_bytevector(pic_state *pic)
     pic_assert_type(pic, e, int);
 
     if (pic_int(pic, e) < 0 || pic_int(pic, e) > 255)
-      pic_errorf(pic, "byte out of range");
+      pic_error(pic, "byte out of range", 0);
 
     *data++ = (unsigned char)pic_int(pic, e);
   }
diff --git a/extlib/benz/bool.c b/extlib/benz/bool.c
index 9de94abc..ee9c52a3 100644
--- a/extlib/benz/bool.c
+++ b/extlib/benz/bool.c
@@ -72,7 +72,7 @@ internal_equal_p(pic_state *pic, pic_value x, pic_value y, int depth, khash_t(m)
 
   if (depth > 10) {
     if (depth > 200) {
-      pic_errorf(pic, "Stack overflow in equal\n");
+      pic_error(pic, "stack overflow in equal", 0);
     }
     if (pic_pair_p(pic, x) || pic_vec_p(pic, x)) {
       int ret;
diff --git a/extlib/benz/char.c b/extlib/benz/char.c
index d4d4b499..7f9d7666 100644
--- a/extlib/benz/char.c
+++ b/extlib/benz/char.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/extra.h"
 
 static pic_value
 pic_char_char_p(pic_state *pic)
@@ -32,7 +33,7 @@ pic_char_integer_to_char(pic_state *pic)
   pic_get_args(pic, "i", &i);
 
   if (i < 0 || i > 255) {
-    pic_errorf(pic, "integer->char: integer out of char range: %d", i);
+    pic_error(pic, "integer->char: integer out of char range", 1, pic_int_value(pic, i));
   }
   
   return pic_char_value(pic, (char)i);
@@ -49,15 +50,13 @@ pic_char_integer_to_char(pic_state *pic)
     pic_get_args(pic, "cc*", &c, &d, &argc, &argv);	\
     							\
     if (! (c op d))					\
-      return pic_false_value(pic);				\
-    							\
-    for (i = 0; i < argc; ++i) {			\
+      return pic_false_value(pic);                      \
+                                                        \
+    for (i = 0; i < argc; ++i) {                        \
       c = d;                                            \
-      if (pic_char_p(pic, argv[i]))                          \
-        d = pic_char(pic, argv[i]);                          \
-      else						\
-	pic_errorf(pic, #op ": char required");         \
-      							\
+      pic_assert_type(pic, argv[i], char);              \
+      d = pic_char(pic, argv[i]);                       \
+                                                        \
       if (! (c op d))					\
 	return pic_false_value(pic);			\
     }							\
diff --git a/extlib/benz/cont.c b/extlib/benz/cont.c
index 0149e00f..64f269a2 100644
--- a/extlib/benz/cont.c
+++ b/extlib/benz/cont.c
@@ -131,7 +131,7 @@ cont_call(pic_state *pic)
     }
   }
   if (cc == NULL) {
-    pic_errorf(pic, "calling dead escape continuation");
+    pic_error(pic, "calling dead escape continuation", 0);
   }
 
   cont->retc = argc;
diff --git a/extlib/benz/dict.c b/extlib/benz/dict.c
index 47a92fd6..34f40de7 100644
--- a/extlib/benz/dict.c
+++ b/extlib/benz/dict.c
@@ -26,7 +26,7 @@ pic_dict_ref(pic_state *pic, pic_value dict, pic_value key)
 
   it = kh_get(dict, h, pic_sym_ptr(pic, key));
   if (it == kh_end(h)) {
-    pic_errorf(pic, "element not found for a key: ~s", key);
+    pic_error(pic, "element not found for given key", 1, key);
   }
   return kh_val(h, it);
 }
@@ -64,7 +64,7 @@ pic_dict_del(pic_state *pic, pic_value dict, pic_value key)
 
   it = kh_get(dict, h, pic_sym_ptr(pic, key));
   if (it == kh_end(h)) {
-    pic_errorf(pic, "no slot named ~s found in dictionary", key);
+    pic_error(pic, "element not found for given key", 1, key);
   }
   kh_del(dict, h, it);
 }
diff --git a/extlib/benz/error.c b/extlib/benz/error.c
index 1111567f..3012fc58 100644
--- a/extlib/benz/error.c
+++ b/extlib/benz/error.c
@@ -37,19 +37,16 @@ pic_warnf(pic_state *pic, const char *fmt, ...)
 }
 
 void
-pic_errorf(pic_state *pic, const char *fmt, ...)
+pic_error(pic_state *pic, const char *msg, int n, ...)
 {
   va_list ap;
-  const char *msg;
-  pic_value err;
+  pic_value irrs;
 
-  va_start(ap, fmt);
-  err = pic_vstrf_value(pic, fmt, ap);
+  va_start(ap, n);
+  irrs = pic_vlist(pic, n, ap);
   va_end(ap);
 
-  msg = pic_str(pic, err);
-
-  pic_raise(pic, pic_make_error(pic, "", msg, pic_nil_value(pic)));
+  pic_raise(pic, pic_make_error(pic, "", msg, irrs));
 }
 
 void
@@ -151,7 +148,7 @@ pic_raise(pic_state *pic, pic_value err)
 
   pic_pop_handler(pic);
 
-  pic_errorf(pic, "error handler returned with ~s on error ~s", val, err);
+  pic_error(pic, "error handler returned", 2, val, err);
 }
 
 static pic_value
diff --git a/extlib/benz/eval.c b/extlib/benz/eval.c
index 41e60d4b..2564f60c 100644
--- a/extlib/benz/eval.c
+++ b/extlib/benz/eval.c
@@ -159,7 +159,7 @@ expand_defmacro(pic_state *pic, pic_value expr, pic_value env)
 
   val = pic_call(pic, pic_compile(pic, pic_expand(pic, pic_list_ref(pic, expr, 2), env)), 0);
   if (! pic_proc_p(pic, val)) {
-    pic_errorf(pic, "macro definition \"~s\" evaluates to non-procedure object", pic_list_ref(pic, expr, 1));
+    pic_error(pic, "macro definition evaluates to non-procedure object", 1, pic_list_ref(pic, expr, 1));
   }
 
   define_macro(pic, uid, val);
@@ -179,7 +179,7 @@ expand_node(pic_state *pic, pic_value expr, pic_value env, pic_value deferred)
     pic_value mac;
 
     if (! pic_list_p(pic, expr)) {
-      pic_errorf(pic, "cannot expand improper list: ~s", expr);
+      pic_error(pic, "cannot expand improper list", 1, expr);
     }
 
     if (pic_id_p(pic, pic_car(pic, expr))) {
@@ -516,7 +516,7 @@ analyze_node(pic_state *pic, analyze_scope *scope, pic_value obj)
     pic_value proc;
 
     if (! pic_list_p(pic, obj)) {
-      pic_errorf(pic, "invalid expression given: ~s", obj);
+      pic_error(pic, "invalid expression given", 1, obj);
     }
 
     proc = pic_list_ref(pic, obj, 0);
@@ -1023,7 +1023,7 @@ codegen(pic_state *pic, codegen_context *cxt, pic_value obj, bool tailpos)
     codegen_call(pic, cxt, obj, tailpos);
   }
   else {
-    pic_errorf(pic, "codegen: unknown AST type ~s", obj);
+    pic_error(pic, "codegen: unknown AST type", 1, obj);
   }
 }
 
diff --git a/extlib/benz/include/picrin.h b/extlib/benz/include/picrin.h
index f255d2e3..b5e63b05 100644
--- a/extlib/benz/include/picrin.h
+++ b/extlib/benz/include/picrin.h
@@ -100,7 +100,7 @@ typedef void (*pic_panicf)(pic_state *, const char *msg);
 
 pic_panicf pic_atpanic(pic_state *, pic_panicf f);
 PIC_NORETURN void pic_panic(pic_state *, const char *msg);
-PIC_NORETURN void pic_errorf(pic_state *, const char *fmt, ...);
+PIC_NORETURN void pic_error(pic_state *, const char *msg, int n, ...);
 PIC_NORETURN void pic_raise(pic_state *, pic_value v);
 pic_value pic_make_error(pic_state *, const char *type, const char *msg, pic_value irrs);
 
diff --git a/extlib/benz/include/picrin/extra.h b/extlib/benz/include/picrin/extra.h
index ed8ea6cb..a7cd6f88 100644
--- a/extlib/benz/include/picrin/extra.h
+++ b/extlib/benz/include/picrin/extra.h
@@ -59,9 +59,9 @@ pic_value pic_fdisplay(pic_state *, pic_value, xFILE *);
 #define pic_push(pic, item, place) (place = pic_cons(pic, item, place))
 #define pic_pop(pic, place) (place = pic_cdr(pic, place))
 
-#define pic_assert_type(pic, v, type) do {                      \
-    if (! pic_##type##_p(pic, v))                               \
-      pic_errorf(pic, "expected " #type ", but got ~s", v);     \
+#define pic_assert_type(pic, v, type) do {      \
+    if (! pic_##type##_p(pic, v))               \
+      pic_error(pic, #type " required", 1, v);  \
   } while (0)
 
 #define pic_void(exec) pic_void_(PIC_GENSYM(ai), exec)
diff --git a/extlib/benz/include/picrin/private/object.h b/extlib/benz/include/picrin/private/object.h
index ec0ec402..2dedfcec 100644
--- a/extlib/benz/include/picrin/private/object.h
+++ b/extlib/benz/include/picrin/private/object.h
@@ -159,16 +159,16 @@ pic_value pic_obj_value(void *ptr);
 struct object *pic_obj_alloc(pic_state *, size_t, int type);
 
 #define VALID_INDEX(pic, len, i) do {                                   \
-    if (i < 0 || len <= i) pic_errorf(pic, "index out of range: %d", i); \
+    if (i < 0 || len <= i) pic_error(pic, "index out of range", 1, pic_int_value(pic, i)); \
   } while (0)
 #define VALID_RANGE(pic, len, s, e) do {                                \
-    if (s < 0 || len < s) pic_errorf(pic, "invalid start index: %d", s); \
-    if (e < s || len < e) pic_errorf(pic, "invalid end index: %d", e);  \
+    if (s < 0 || len < s) pic_error(pic, "invalid start index", 1, pic_int_value(pic, s)); \
+    if (e < s || len < e) pic_error(pic, "invalid end index", 1, pic_int_value(pic, e)); \
   } while (0)
-#define VALID_ATRANGE(pic, tolen, at, fromlen, s, e) do {       \
-    VALID_INDEX(pic, tolen, at);                                \
-    VALID_RANGE(pic, fromlen, s, e);                            \
-    if (tolen - at < e - s) pic_errorf(pic, "invalid range");   \
+#define VALID_ATRANGE(pic, tolen, at, fromlen, s, e) do {               \
+    VALID_INDEX(pic, tolen, at);                                        \
+    VALID_RANGE(pic, fromlen, s, e);                                    \
+    if (tolen - at < e - s) pic_error(pic, "invalid range", 0);        \
   } while (0)
 
 pic_value pic_make_identifier(pic_state *, pic_value id, pic_value env);
diff --git a/extlib/benz/lib.c b/extlib/benz/lib.c
index c1266d77..b200b4cb 100644
--- a/extlib/benz/lib.c
+++ b/extlib/benz/lib.c
@@ -127,7 +127,7 @@ get_library(pic_state *pic, const char *lib)
   struct lib *libp;
 
   if ((libp = get_library_opt(pic, lib)) == NULL) {
-    pic_errorf(pic, "library not found: %s", lib);
+    pic_error(pic, "library not found", 1, pic_cstr_value(pic, lib));
   }
   return libp;
 }
@@ -175,7 +175,7 @@ pic_make_library(pic_state *pic, const char *lib)
 
   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);
+    pic_error(pic, "library name already in use", pic_cstr_value(pic, lib));
   }
 
   kh_val(h, it).name = pic_str_ptr(pic, name);
@@ -223,7 +223,7 @@ pic_import(pic_state *pic, const char *lib)
   while (pic_dict_next(pic, pic_obj_value(libp->exports), &it, &name, &realname)) {
     uid = pic_find_identifier(pic, realname, pic_obj_value(libp->env));
     if (! pic_weak_has(pic, pic->globals, uid) && ! pic_weak_has(pic, pic->macros, uid)) {
-      pic_errorf(pic, "attempted to export undefined variable '~s'", realname);
+      pic_error(pic, "attempted to export undefined variable", 1, realname);
     }
     pic_put_identifier(pic, name, uid, pic_obj_value(pic->lib->env));
   }
@@ -292,14 +292,14 @@ pic_lib_library_import(pic_state *pic)
   libp = get_library(pic, lib);
 
   if (! pic_dict_has(pic, pic_obj_value(libp->exports), name)) {
-    pic_errorf(pic, "library-import: variable is not exported '~s'", name);
+    pic_error(pic, "library-import: variable is not exported", 1, name);
   } else {
     realname = pic_dict_ref(pic, pic_obj_value(libp->exports), name);
   }
 
   uid = pic_find_identifier(pic, realname, pic_obj_value(libp->env));
   if (! pic_weak_has(pic, pic->globals, uid) && ! pic_weak_has(pic, pic->macros, uid)) {
-    pic_errorf(pic, "attempted to export undefined variable '~s'", realname);
+    pic_error(pic, "attempted to export undefined variable", 1, realname);
   }
 
   pic_put_identifier(pic, alias, uid, pic_obj_value(pic->lib->env));
diff --git a/extlib/benz/number.c b/extlib/benz/number.c
index 2c6d8d37..2ecbe2d9 100644
--- a/extlib/benz/number.c
+++ b/extlib/benz/number.c
@@ -59,7 +59,6 @@ pic_number_exact(pic_state *pic)
   pic_value                                                             \
   name(pic_state *pic, pic_value a, pic_value b)                        \
   {                                                                     \
-    PIC_NORETURN void pic_errorf(pic_state *, const char *, ...);       \
     double f;                                                           \
     if (pic_int_p(pic, a) && pic_int_p(pic, b)) {                       \
       f = (double)pic_int(pic, a) op (double)pic_int(pic, b);           \
@@ -73,7 +72,7 @@ pic_number_exact(pic_state *pic)
     } else if (pic_float_p(pic, a) && pic_int_p(pic, b)) {              \
       return pic_float_value(pic, pic_float(pic, a) op pic_int(pic, b)); \
     } else {                                                            \
-      pic_errorf(pic, #name ": non-number operand given");              \
+      pic_error(pic, #name ": non-number operand given", 0);              \
     }                                                                   \
     PIC_UNREACHABLE();                                                  \
   }
@@ -87,7 +86,6 @@ pic_define_aop(pic_div, /, f == (int)f)
   bool                                                                  \
   name(pic_state *pic, pic_value a, pic_value b)                        \
   {                                                                     \
-    PIC_NORETURN void pic_errorf(pic_state *, const char *, ...);       \
     if (pic_int_p(pic, a) && pic_int_p(pic, b)) {                       \
       return pic_int(pic, a) op pic_int(pic, b);                        \
     } else if (pic_float_p(pic, a) && pic_float_p(pic, b)) {            \
@@ -97,7 +95,7 @@ pic_define_aop(pic_div, /, f == (int)f)
     } else if (pic_float_p(pic, a) && pic_int_p(pic, b)) {              \
       return pic_float(pic, a) op pic_int(pic, b);                      \
     } else {                                                            \
-      pic_errorf(pic, #name ": non-number operand given");              \
+      pic_error(pic, #name ": non-number operand given", 0);              \
     }                                                                   \
     PIC_UNREACHABLE();                                                  \
   }
@@ -165,10 +163,10 @@ DEFINE_AOP(mul, argv[0], do {
     return pic_int_value(pic, 1);
   } while (0))
 DEFINE_AOP(sub, pic_sub(pic, pic_int_value(pic, 0), argv[0]), do {
-    pic_errorf(pic, "-: at least one argument required");
+    pic_error(pic, "-: at least one argument required", 0);
   } while (0))
 DEFINE_AOP(div, pic_div(pic, pic_int_value(pic, 1), argv[0]), do {
-    pic_errorf(pic, "/: at least one argument required");
+    pic_error(pic, "/: at least one argument required", 0);
   } while (0))
 
 static int
@@ -224,7 +222,7 @@ pic_number_number_to_string(pic_state *pic)
   pic_get_args(pic, "F|i", &f, &e, &radix);
 
   if (radix < 2 || radix > 36) {
-    pic_errorf(pic, "number->string: invalid radix %d (between 2 and 36, inclusive)", radix);
+    pic_error(pic, "number->string: invalid radix (between 2 and 36, inclusive)", 1, pic_int_value(pic, radix));
   }
 
   if (e) {
diff --git a/extlib/benz/pair.c b/extlib/benz/pair.c
index 4d6f474a..4e7c27b3 100644
--- a/extlib/benz/pair.c
+++ b/extlib/benz/pair.c
@@ -22,7 +22,7 @@ pic_value
 pic_car(pic_state *pic, pic_value obj)
 {
   if (! pic_pair_p(pic, obj)) {
-    pic_errorf(pic, "car: pair required, but got ~s", obj);
+    pic_error(pic, "car: pair required", 1, obj);
   }
   return pic_pair_ptr(pic, obj)->car;
 }
@@ -31,7 +31,7 @@ pic_value
 pic_cdr(pic_state *pic, pic_value obj)
 {
   if (! pic_pair_p(pic, obj)) {
-    pic_errorf(pic, "cdr: pair required, but got ~s", obj);
+    pic_error(pic, "cdr: pair required", 1, obj);
   }
   return pic_pair_ptr(pic, obj)->cdr;
 }
@@ -40,7 +40,7 @@ void
 pic_set_car(pic_state *pic, pic_value obj, pic_value val)
 {
   if (! pic_pair_p(pic, obj)) {
-    pic_errorf(pic, "pair required");
+    pic_error(pic, "pair required", 0);
   }
   pic_pair_ptr(pic, obj)->car = val;
 }
@@ -49,7 +49,7 @@ void
 pic_set_cdr(pic_state *pic, pic_value obj, pic_value val)
 {
   if (! pic_pair_p(pic, obj)) {
-    pic_errorf(pic, "pair required");
+    pic_error(pic, "pair required", 0);
   }
   pic_pair_ptr(pic, obj)->cdr = val;
 }
@@ -171,15 +171,10 @@ pic_length(pic_state *pic, pic_value obj)
 {
   int c = 0;
 
-  if (! pic_list_p(pic, obj)) {
-    pic_errorf(pic, "length: expected list, but got ~s", obj);
-  }
-
   while (! pic_nil_p(pic, obj)) {
     obj = pic_cdr(pic, obj);
     ++c;
   }
-
   return c;
 }
 
@@ -477,7 +472,7 @@ pic_pair_map(pic_state *pic)
   pic_get_args(pic, "l*", &proc, &argc, &args);
 
   if (argc == 0)
-    pic_errorf(pic, "map: wrong number of arguments (1 for at least 2)");
+    pic_error(pic, "map: wrong number of arguments (1 for at least 2)", 0);
 
   arg_list = pic_alloca(pic, sizeof(pic_value) * argc);
 
diff --git a/extlib/benz/port.c b/extlib/benz/port.c
index a0c70e6a..f4d80092 100644
--- a/extlib/benz/port.c
+++ b/extlib/benz/port.c
@@ -36,7 +36,7 @@ pic_close_port(pic_state *pic, pic_value port)
     return;
   }
   if (xfclose(pic, file) == EOF) {
-    pic_errorf(pic, "close-port: failure");
+    pic_error(pic, "close-port: failure", 0);
   }
 }
 
@@ -123,13 +123,13 @@ pic_port_close_port(pic_state *pic)
     if ((pic_fileno(pic, port)->flag & (flags)) != (flags)) {                      \
       switch (flags) {                                                  \
       case X_WRITE:                                                     \
-        pic_errorf(pic, caller ": expected output port");               \
+        pic_error(pic, caller ": output port required", 0);               \
       case X_READ:                                                      \
-        pic_errorf(pic, caller ": expected input port");                \
+        pic_error(pic, caller ": input port required", 0);                \
       }                                                                 \
     }                                                                   \
     if (pic_fileno(pic, port)->flag == 0) {                                        \
-      pic_errorf(pic, caller ": expected open port");                   \
+      pic_error(pic, caller ": open port required", 0);                   \
     }                                                                   \
   } while (0)
 
@@ -164,7 +164,7 @@ pic_port_get_output_bytevector(pic_state *pic)
   assert_port_profile(port, X_WRITE, "get-output-bytevector");
 
   if (xfget_buf(pic, pic_fileno(pic, port), &buf, &len) < 0) {
-    pic_errorf(pic, "port was not created by open-output-bytevector");
+    pic_error(pic, "port was not created by open-output-bytevector", 0);
   }
   return pic_blob_value(pic, (unsigned char *)buf, len);
 }
diff --git a/extlib/benz/proc.c b/extlib/benz/proc.c
index 570f1730..66061ade 100644
--- a/extlib/benz/proc.c
+++ b/extlib/benz/proc.c
@@ -10,6 +10,16 @@
 
 #define MIN(x,y) ((x) < (y) ? (x) : (y))
 
+PIC_NORETURN static void
+arg_error(pic_state *pic, int actual, bool varg, int expected)
+{
+  const char *msg;
+
+  msg = pic_str(pic, pic_strf_value(pic, "wrong number of arguments (%d for %s%d)", actual, (varg ? "at least " : ""), expected));
+
+  pic_error(pic, msg, 0);
+}
+
 #define GET_OPERAND(pic,n) ((pic)->ci->fp[(n)])
 
 /**
@@ -80,7 +90,7 @@ pic_get_args(pic_state *pic, const char *format, ...)
   }
 
   if (argc < paramc || (paramc + optc < argc && ! rest)) {
-    pic_errorf(pic, "pic_get_args: wrong number of arguments (%d for %s%d)", argc, rest? "at least " : "", paramc);
+    arg_error(pic, argc, rest, paramc);
   }
 
   va_start(ap, format);
@@ -121,7 +131,9 @@ pic_get_args(pic_state *pic, const char *format, ...)
         *data = pic_data(pic, v);
       }
       else {
-        pic_errorf(pic, "pic_get_args: expected data type \"%s\", but got ~s", type->type_name, v);
+        const char *msg;
+        msg = pic_str(pic, pic_strf_value(pic, "pic_get_args: data type \"%s\" required", type->type_name));
+        pic_error(pic, msg, 1, v);
       }
       break;
     }
@@ -139,7 +151,7 @@ pic_get_args(pic_state *pic, const char *format, ...)
         if (buf) *buf = tmp;
       }
       else {
-        pic_errorf(pic, "pic_get_args: expected bytevector, but got ~s", v);
+        pic_error(pic, "pic_get_args: bytevector required", 1, v);
       }
       break;
     }
@@ -155,16 +167,16 @@ pic_get_args(pic_state *pic, const char *format, ...)
                                                                         \
         v = GET_OPERAND(pic, i);                                        \
         switch (pic_type(pic, v)) {                                     \
-        case PIC_TYPE_FLOAT:                                              \
+        case PIC_TYPE_FLOAT:                                            \
           *n = pic_float(pic, v);                                       \
           *e = false;                                                   \
           break;                                                        \
-        case PIC_TYPE_INT:                                                \
+        case PIC_TYPE_INT:                                              \
           *n = pic_int(pic, v);                                         \
           *e = true;                                                    \
           break;                                                        \
         default:                                                        \
-          pic_errorf(pic, "pic_get_args: expected float or int, but got ~s", v); \
+          pic_error(pic, "pic_get_args: float or int required", 1, v);  \
         }                                                               \
         break;                                                          \
       }
@@ -183,7 +195,7 @@ pic_get_args(pic_state *pic, const char *format, ...)
           *ptr = conv;                                                  \
         }                                                               \
         else {                                                          \
-          pic_errorf(pic, "pic_get_args: expected " #type ", but got ~s", v); \
+          pic_error(pic, "pic_get_args: " #type " required", 1, v);     \
         }                                                               \
         break;                                                          \
       }
@@ -202,7 +214,7 @@ pic_get_args(pic_state *pic, const char *format, ...)
     OBJ_CASE('r', rec)
 
     default:
-      pic_errorf(pic, "pic_get_args: invalid argument specifier '%c' given", c);
+      pic_error(pic, "pic_get_args: invalid argument specifier given", 1, pic_char_value(pic, c));
     }
 
     if (format[1] == '+') {
@@ -232,11 +244,11 @@ vm_gref(pic_state *pic, pic_value uid)
   pic_value val;
 
   if (! pic_weak_has(pic, pic->globals, uid)) {
-    pic_errorf(pic, "undefined variable ~s", uid);
+    pic_error(pic, "undefined variable", 1, uid);
   }
   val = pic_weak_ref(pic, pic->globals, uid);;
   if (pic_invalid_p(pic, val)) {
-    pic_errorf(pic, "uninitialized global variable: ~s", uid);
+    pic_error(pic, "uninitialized global variable", 1, uid);
   }
   return val;
 }
@@ -245,7 +257,7 @@ static void
 vm_gset(pic_state *pic, pic_value uid, pic_value value)
 {
   if (! pic_weak_has(pic, pic->globals, uid)) {
-    pic_errorf(pic, "undefined variable ~s", uid);
+    pic_error(pic, "undefined variable", 1, uid);
   }
   pic_weak_set(pic, pic->globals, uid, value);
 }
@@ -488,7 +500,7 @@ pic_apply(pic_state *pic, pic_value proc, int argc, pic_value *argv)
     L_CALL:
       x = pic->sp[-c.a];
       if (! pic_proc_p(pic, x)) {
-	pic_errorf(pic, "invalid application: ~s", x);
+	pic_error(pic, "invalid application", 1, x);
       }
       proc = pic_proc_ptr(pic, x);
 
@@ -521,7 +533,7 @@ pic_apply(pic_state *pic, pic_value proc, int argc, pic_value *argv)
         ci->irep = irep;
 	if (ci->argc != irep->argc) {
 	  if (! (irep->varg && ci->argc >= irep->argc)) {
-            pic_errorf(pic, "wrong number of arguments (%d for %s%d)", ci->argc - 1, (irep->varg ? "at least " : ""), irep->argc - 1);
+            arg_error(pic, ci->argc - 1, irep->varg, irep->argc - 1);
 	  }
 	}
 	/* prepare rest args */
@@ -909,7 +921,7 @@ pic_closure_ref(pic_state *pic, int n)
   assert(pic_func_p(self));
 
   if (n < 0 || pic_proc_ptr(pic, self)->u.f.localc <= n) {
-    pic_errorf(pic, "pic_closure_ref: index out of range (%d)", n);
+    pic_error(pic, "pic_closure_ref: index out of range", 1, pic_int_value(pic, n));
   }
   return pic_proc_ptr(pic, self)->locals[n];
 }
@@ -922,7 +934,7 @@ pic_closure_set(pic_state *pic, int n, pic_value v)
   assert(pic_func_p(self));
 
   if (n < 0 || pic_proc_ptr(pic, self)->u.f.localc <= n) {
-    pic_errorf(pic, "pic_closure_ref: index out of range (%d)", n);
+    pic_error(pic, "pic_closure_ref: index out of range", 1, pic_int_value(pic, n));
   }
   pic_proc_ptr(pic, self)->locals[n] = v;
 }
@@ -1019,7 +1031,7 @@ pic_proc_apply(pic_state *pic)
   pic_get_args(pic, "l*", &proc, &argc, &args);
 
   if (argc == 0) {
-    pic_errorf(pic, "apply: wrong number of arguments");
+    pic_error(pic, "apply: wrong number of arguments", 0);
   }
 
   n = argc - 1 + pic_length(pic, args[argc - 1]);
diff --git a/extlib/benz/string.c b/extlib/benz/string.c
index 75a703db..d08f6178 100644
--- a/extlib/benz/string.c
+++ b/extlib/benz/string.c
@@ -276,7 +276,7 @@ pic_str_ref(pic_state *pic, pic_value str, int i)
 
   c = rope_at(pic_str_ptr(pic, str)->rope, i);
   if (c == -1) {
-    pic_errorf(pic, "index out of range %d", i);
+    pic_error(pic, "index out of range", 1, pic_int_value(pic, i));
   }
   return (char)c;
 }
@@ -453,7 +453,7 @@ pic_str_make_string(pic_state *pic)
   pic_get_args(pic, "i|c", &len, &c);
 
   if (len < 0) {
-    pic_errorf(pic, "make-string: negative length given %d", len);
+    pic_error(pic, "make-string: negative length given", 1, pic_int_value(pic, len));
   }
 
   buf = pic_alloca(pic, len);
@@ -647,7 +647,7 @@ pic_str_string_map(pic_state *pic)
   pic_get_args(pic, "l*", &proc, &argc, &argv);
 
   if (argc == 0) {
-    pic_errorf(pic, "string-map: one or more strings expected, but got zero");
+    pic_error(pic, "string-map: one or more strings expected, but got zero", 0);
   }
 
   len = INT_MAX;
@@ -684,7 +684,7 @@ pic_str_string_for_each(pic_state *pic)
   pic_get_args(pic, "l*", &proc, &argc, &argv);
 
   if (argc == 0) {
-    pic_errorf(pic, "string-map: one or more strings expected, but got zero");
+    pic_error(pic, "string-map: one or more strings expected, but got zero", 0);
   }
 
   len = INT_MAX;
diff --git a/extlib/benz/symbol.c b/extlib/benz/symbol.c
index cff34df8..f67f7593 100644
--- a/extlib/benz/symbol.c
+++ b/extlib/benz/symbol.c
@@ -146,7 +146,7 @@ pic_symbol_identifier_base(pic_state *pic)
   pic_assert_type(pic, id, id);
 
   if (pic_sym_p(pic, id)) {
-    pic_errorf(pic, "expected non-symbol identifier, but got symbol ~s", id);
+    pic_error(pic, "non-symbol identifier required", 1, id);
   }
 
   return pic_obj_value(pic_id_ptr(pic, id)->u.id);
@@ -162,7 +162,7 @@ pic_symbol_identifier_environment(pic_state *pic)
   pic_assert_type(pic, id, id);
 
   if (pic_sym_p(pic, id)) {
-    pic_errorf(pic, "expected non-symbol identifier, but got symbol ~s", id);
+    pic_error(pic, "non-symbol identifier required", 1, id);
   }
 
   return pic_obj_value(pic_id_ptr(pic, id)->env);
diff --git a/extlib/benz/value.c b/extlib/benz/value.c
index a41d7d52..32b17d65 100644
--- a/extlib/benz/value.c
+++ b/extlib/benz/value.c
@@ -256,6 +256,6 @@ pic_typename(pic_state *pic, int type)
   case PIC_TYPE_CP:
     return "checkpoint";
   default:
-    pic_errorf(pic, "pic_typename: invalid type given %d", type);
+    pic_error(pic, "pic_typename: invalid type given", 1, pic_int_value(pic, type));
   }
 }
diff --git a/extlib/benz/vector.c b/extlib/benz/vector.c
index 978cfeb1..781d138a 100644
--- a/extlib/benz/vector.c
+++ b/extlib/benz/vector.c
@@ -73,7 +73,7 @@ pic_vec_make_vector(pic_state *pic)
   n = pic_get_args(pic, "i|o", &k, &init);
 
   if (k < 0) {
-    pic_errorf(pic, "make-vector: negative length given %d", k);
+    pic_error(pic, "make-vector: negative length given", 1, pic_int_value(pic, k));
   }
 
   vec = pic_make_vec(pic, k, NULL);
@@ -231,7 +231,7 @@ pic_vec_vector_map(pic_state *pic)
   pic_get_args(pic, "l*", &proc, &argc, &argv);
 
   if (argc == 0) {
-    pic_errorf(pic, "vector-map: wrong number of arguments (1 for at least 2)");
+    pic_error(pic, "vector-map: wrong number of arguments (1 for at least 2)", 0);
   }
 
   len = INT_MAX;
@@ -265,7 +265,7 @@ pic_vec_vector_for_each(pic_state *pic)
   pic_get_args(pic, "l*", &proc, &argc, &argv);
 
   if (argc == 0) {
-    pic_errorf(pic, "vector-for-each: wrong number of arguments (1 for at least 2)");
+    pic_error(pic, "vector-for-each: wrong number of arguments (1 for at least 2)", 0);
   }
 
   len = INT_MAX;
diff --git a/extlib/benz/weak.c b/extlib/benz/weak.c
index 3064873c..722d153b 100644
--- a/extlib/benz/weak.c
+++ b/extlib/benz/weak.c
@@ -27,7 +27,7 @@ pic_weak_ref(pic_state *pic, pic_value weak, pic_value key)
 
   it = kh_get(weak, h, pic_obj_ptr(key));
   if (it == kh_end(h)) {
-    pic_errorf(pic, "element not found for a key: ~s", key);
+    pic_error(pic, "element not found for given key", 1, key);
   }
   return kh_val(h, it);
 }
@@ -59,7 +59,7 @@ pic_weak_del(pic_state *pic, pic_value weak, pic_value key)
 
   it = kh_get(weak, h, pic_obj_ptr(key));
   if (it == kh_end(h)) {
-    pic_errorf(pic, "no slot named ~s found in ephemeron", key);
+    pic_error(pic, "element not found for given key", 1, key);
   }
   kh_del(weak, h, it);
 }
@@ -74,7 +74,7 @@ weak_call(pic_state *pic)
   n = pic_get_args(pic, "o|o", &key, &val);
 
   if (! pic_obj_p(pic, key)) {
-    pic_errorf(pic, "attempted to set a non-object key '~s' in an ephemeron", key);
+    pic_error(pic, "attempted to set a non-object key", 1, key);
   }
 
   weak = pic_closure_ref(pic, 0);