diff --git a/lib/bigint.c b/lib/bigint.c
index 1e9b777..ffdc5c9 100644
--- a/lib/bigint.c
+++ b/lib/bigint.c
@@ -38,7 +38,7 @@
 #define IS_POW2(ui) (((ui) > 0) && ((ui) & ((ui) - 1)) == 0)
 
 /* digit character array */
-static char* _digitc_array[] =
+static const char* _digitc_array[] =
 {
 	"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ",
 	"0123456789abcdefghijklmnopqrstuvwxyz"
diff --git a/lib/comp.c b/lib/comp.c
index 2d6d538..6c4f56e 100644
--- a/lib/comp.c
+++ b/lib/comp.c
@@ -4625,11 +4625,12 @@ static HCL_INLINE int compile_dsymbol (hcl_t* hcl, hcl_cnode_t* obj)
 
 HCL_UNUSED static int string_to_ooi (hcl_t* hcl, hcl_oocs_t* str, int radixed, hcl_ooi_t* num)
 {
-	/* it is not a generic conversion function.
+	/* [NOTE]
+	 * it is not a generic conversion functionu
 	 * it assumes a certain pre-sanity check on the string
 	 * done by the lexical analyzer */
 
-	int v, negsign, base;
+	int v, negsign, base = 10;
 	const hcl_ooch_t* ptr, * end;
 	hcl_oow_t value, old_value;
 
@@ -4647,26 +4648,43 @@ HCL_UNUSED static int string_to_ooi (hcl_t* hcl, hcl_oocs_t* str, int radixed, h
 
 	if (radixed)
 	{
+		/* 0xFF80, 0b1111 */
 		HCL_ASSERT (hcl, ptr < end);
 
-		if (*ptr != '#')
+		if (*ptr == '0')
 		{
-			hcl_seterrbfmt (hcl, HCL_EINVAL, "radixed number not starting with # - %*.js", str->len, str->ptr);
-			return -1;
-		}
-		ptr++; /* skip '#' */
+			ptr++;
+			HCL_ASSERT (hcl, ptr < end);
 
-		if (*ptr == 'x') base = 16;
-		else if (*ptr == 'o') base = 8;
-		else if (*ptr == 'b') base = 2;
-		else
+			if (*ptr == 'x') base = 16;
+			else if (*ptr == 'o') base = 8;
+			else if (*ptr == 'b') base = 2;
+			else goto radix_r;
+
+			ptr++;
+		}
+
+		if (base == 10)
 		{
-			hcl_seterrbfmt (hcl, HCL_EINVAL, "invalid radix specifier - %c", *ptr);
+		radix_r:
+			base = 0;
+			do
+			{
+				base = base * 10 + HCL_CHAR_TO_NUM(*ptr, 10);
+				ptr++;
+			}
+			while (*ptr != 'r');
+			ptr++;
+		}
+
+		if (base < 2 || base > 36)
+		{
+		invalid_radix_value:
+			hcl_seterrbfmt (hcl, HCL_EINVAL,
+				"invalid radix value '%d' in radixed number '%.*js'", base, str->len, str->ptr);
 			return -1;
 		}
-		ptr++;
 	}
-	else base = 10;
 
 	HCL_ASSERT (hcl, ptr < end);
 
@@ -4705,13 +4723,17 @@ HCL_UNUSED static int string_to_ooi (hcl_t* hcl, hcl_oocs_t* str, int radixed, h
 
 static hcl_oop_t string_to_num (hcl_t* hcl, hcl_oocs_t* str, const hcl_loc_t* loc, int radixed)
 {
-	int negsign, base;
+	int negsign, base = 10;
 	const hcl_ooch_t* ptr, * end;
 
 	negsign = 0;
 	ptr = str->ptr,
 	end = str->ptr + str->len;
 
+	/* [NOTE]
+	 *   The code here assumes that the reader ensures that
+	 *   there is at least 1 valid digit after radix specifier. */
+
 	HCL_ASSERT (hcl, ptr < end);
 
 	if (*ptr == '+' || *ptr == '-')
@@ -4720,48 +4742,46 @@ static hcl_oop_t string_to_num (hcl_t* hcl, hcl_oocs_t* str, const hcl_loc_t* lo
 		ptr++;
 	}
 
-#if 0
-	if (radixed)
-	{
-		/* 16r1234, 2r1111 */
-		HCL_ASSERT (hcl, ptr < end);
-
-		base = 0;
-		do
-		{
-			base = base * 10 + HCL_CHAR_TO_NUM(*ptr, 10);
-			ptr++;
-		}
-		while (*ptr != 'r');
-
-		ptr++;
-	}
-	else base = 10;
-#else
 	if (radixed)
 	{
 		/* 0xFF80, 0b1111 */
 		HCL_ASSERT (hcl, ptr < end);
 
-		if (/**ptr != '#' &&*/ *ptr != '0')
+		if (*ptr == '0')
 		{
-			hcl_setsynerrbfmt(hcl, HCL_SYNERR_RADIX, loc, str, "radixed number not starting with #");
-			return HCL_NULL;
-		}
-		ptr++; /* skip '0' */
+			ptr++;
+			HCL_ASSERT (hcl, ptr < end);
 
-		if (*ptr == 'x') base = 16;
-		else if (*ptr == 'o') base = 8;
-		else if (*ptr == 'b') base = 2;
-		else
+			if (*ptr == 'x') base = 16;
+			else if (*ptr == 'o') base = 8;
+			else if (*ptr == 'b') base = 2;
+			else goto radix_r;
+
+			ptr++;
+		}
+
+
+		if (base == 10)
 		{
-			hcl_setsynerrbfmt (hcl, HCL_SYNERR_RADIX, loc, HCL_NULL, "invalid radix specifier %c in %js", *ptr, str);
+		radix_r:
+			base = 0;
+			do
+			{
+				base = base * 10 + HCL_CHAR_TO_NUM(*ptr, 10);
+				ptr++;
+			}
+			while (*ptr != 'r');
+			ptr++;
+		}
+
+		if (base < 2 || base > 36)
+		{
+		invalid_radix_value:
+			hcl_setsynerrbfmt (hcl, HCL_SYNERR_RADIX, loc, HCL_NULL,
+				"invalid radix value '%d' in radixed number '%.*js'", base, str->len, str->ptr);
 			return HCL_NULL;
 		}
-		ptr++;
 	}
-	else base = 10;
-#endif
 
 /* TODO: handle floating point numbers ... etc */
 	if (negsign) base = -base;
diff --git a/lib/err.c b/lib/err.c
index 4820db2..cb8847a 100644
--- a/lib/err.c
+++ b/lib/err.c
@@ -91,7 +91,7 @@ static hcl_ooch_t* errstr[] =
 };
 
 
-static char* synerrstr[] =
+static const char* synerrstr[] =
 {
 	"no error",
 	"internal error",
diff --git a/lib/exec.c b/lib/exec.c
index e672bdc..9206ac7 100644
--- a/lib/exec.c
+++ b/lib/exec.c
@@ -3301,7 +3301,7 @@ static hcl_oop_t fetch_numeric_rcv_slot (hcl_t* hcl, hcl_oop_t rcv, hcl_oow_t b1
 	hcl_oow_t w;
 	hcl_obj_type_t rcv_type;
 
-	rcv_type = HCL_OBJ_GET_FLAGS_TYPE(rcv);
+	rcv_type = (hcl_obj_type_t)HCL_OBJ_GET_FLAGS_TYPE(rcv);
 	switch (HCL_LIKELY(rcv_type))
 	{
 		case HCL_OBJ_TYPE_CHAR:
@@ -3334,7 +3334,7 @@ static int store_into_numeric_rcv_slot (hcl_t* hcl, hcl_oop_t rcv, hcl_oow_t b1,
 	if (HCL_OOP_IS_CHAR(v)) w = HCL_OOP_TO_CHAR(v);
 	else if (hcl_inttooow(hcl, v, &w) <= -1) return -1;
 
-	rcv_type = HCL_OBJ_GET_FLAGS_TYPE(rcv);
+	rcv_type = (hcl_obj_type_t)HCL_OBJ_GET_FLAGS_TYPE(rcv);
 	switch (HCL_LIKELY(rcv_type))
 	{
 		case HCL_OBJ_TYPE_CHAR:
@@ -4172,7 +4172,7 @@ hcl_logbfmt (hcl, HCL_LOG_STDERR, ">>>%O c->sc=%O sc=%O b2=%d b3=%d nivars=%d nc
 				hcl_oop_t _class;
 				hcl_oop_t mdic, blk, name;
 				int mtype;
-				static hcl_bch_t* pfx[] = { "c", "i", "ci" };
+				static const hcl_bch_t* pfx[] = { "c", "i", "ci" };
 
 				mtype = (bcode - HCL_CODE_CLASS_CMSTORE) + 1;
 				HCL_ASSERT (hcl, mtype >= 1 && mtype <= 3);
diff --git a/lib/hcl-prv.h b/lib/hcl-prv.h
index c9012b2..cccb711 100644
--- a/lib/hcl-prv.h
+++ b/lib/hcl-prv.h
@@ -813,6 +813,9 @@ struct hcl_flx_pn_t
 	/* state data */
 	int fpdec;
 	int radix;
+	int radix_cand_overflown;
+	hcl_oow_t radix_cand;
+	hcl_tok_type_t tok_type;
 	hcl_oow_t digit_count[2];
 	hcl_ooch_t start_digit;
 };
diff --git a/lib/read.c b/lib/read.c
index cbe9c93..1173b32 100644
--- a/lib/read.c
+++ b/lib/read.c
@@ -236,7 +236,6 @@ static HCL_INLINE int is_linebreak (hcl_ooci_t c)
 
 static HCL_INLINE int is_digit_char (hcl_ooci_t c)
 {
-/* TODO: support full unicode */
 	return (c >= '0' && c <= '9');
 }
 
@@ -286,7 +285,7 @@ int hcl_is_binop_char (hcl_ooci_t c) /* not static HCL_INLINE for shared use wit
 	return c == '&' || c == '*' || c == '+' || c == '-' || c == '/' || c == '%' ||
 	       c == '<' || c == '>' || c == '=' || c == '@' || c == '|' || c == '~';
 }
-
+#define is_binop_char(c) hcl_is_binop_char(c)
 
 static HCL_INLINE int is_lead_ident_char (hcl_ooci_t c)
 {
@@ -1061,12 +1060,12 @@ static int chain_to_list (hcl_t* hcl, hcl_cnode_t* obj, hcl_loc_t* loc)
 {
 	hcl_rstl_t* rstl;
 	int flagv;
-	int list_concode;
+	/*int list_concode;*/
 
 	HCL_ASSERT (hcl, hcl->c->r.st != HCL_NULL);
 	rstl = hcl->c->r.st;
 	flagv = rstl->flagv;
-	list_concode = (hcl_concode_t)LIST_FLAG_GET_CONCODE(flagv);
+	/*list_concode = (hcl_concode_t)LIST_FLAG_GET_CONCODE(flagv);*/
 
 	if (flagv & CLOSED)
 	{
@@ -2232,6 +2231,9 @@ static HCL_INLINE void init_flx_pn (hcl_flx_pn_t* pn, hcl_ooch_t start_digit)
 	HCL_MEMSET (pn, 0, HCL_SIZEOF(*pn));
 	pn->start_digit = start_digit;
 	pn->radix = 10;
+	pn->radix_cand = 0;
+	pn->radix_cand_overflown = 0;
+	pn->tok_type = HCL_TOK_NUMLIT;
 }
 
 static HCL_INLINE void init_flx_st (hcl_flx_st_t* st, hcl_ooch_t sign_c)
@@ -2349,7 +2351,7 @@ static int flx_start (hcl_t* hcl, hcl_ooci_t c)
 			FEED_CONTINUE (hcl, HCL_FLX_PLAIN_NUMBER);
 			goto not_consumed;
 
-		case 'B':
+		case 'B': /* for charcter/string prefixed with B,b,C,c */
 		case 'b':
 		case 'C':
 		case 'c':
@@ -2358,7 +2360,7 @@ static int flx_start (hcl_t* hcl, hcl_ooci_t c)
 			goto consumed;
 
 		default:
-			if (hcl_is_binop_char(c))
+			if (is_binop_char(c))
 			{
 				init_flx_binop (FLX_BINOP(hcl));
 				FEED_CONTINUE (hcl, HCL_FLX_BINOP);
@@ -2532,7 +2534,7 @@ static int flx_hmarked_token (hcl_t* hcl, hcl_ooci_t c)
 	 * #"..."   symbol literal
 	 */
 
-	if (hcl_is_binop_char(c))
+	if (is_binop_char(c))
 	{
 		reset_flx_token (hcl);
 		FEED_CONTINUE_WITH_CHAR (hcl, c, HCL_FLX_HMARKED_BINOP);
@@ -2551,6 +2553,7 @@ static int flx_hmarked_token (hcl_t* hcl, hcl_ooci_t c)
 
 		/* --------------------------- */
 
+	#if 0
 		case 'x': /* hexadecimal number */
 			init_flx_hn (FLX_HN(hcl), HCL_TOK_RADNUMLIT, HCL_SYNERR_NUMLIT, 16);
 			goto radixed_number;
@@ -2558,6 +2561,7 @@ static int flx_hmarked_token (hcl_t* hcl, hcl_ooci_t c)
 		case 'o': /* octal number */
 			init_flx_hn (FLX_HN(hcl), HCL_TOK_RADNUMLIT, HCL_SYNERR_NUMLIT, 8);
 			goto radixed_number;
+	#endif
 
 		case 'b': /* binary number or byte array */
 		case 'B':
@@ -2568,6 +2572,7 @@ static int flx_hmarked_token (hcl_t* hcl, hcl_ooci_t c)
 			FEED_CONTINUE_WITH_CHAR (hcl, c, HCL_FLX_HMARKED_BC);
 			break;
 
+	#if 0
 		case 'e': /* #eXXX - error literal */
 			init_flx_hn (FLX_HN(hcl), HCL_TOK_ERRLIT, HCL_SYNERR_ERRLIT, 10);
 			goto radixed_number;
@@ -2577,6 +2582,7 @@ static int flx_hmarked_token (hcl_t* hcl, hcl_ooci_t c)
 		radixed_number:
 			FEED_CONTINUE_WITH_CHAR (hcl, c, HCL_FLX_HMARKED_NUMBER);
 			goto consumed;
+	#endif
 
 		/* --------------------------- */
 		case '\\':
@@ -2728,6 +2734,7 @@ static int flx_hmarked_bc (hcl_t* hcl, hcl_ooci_t c)
 		FEED_WRAP_UP_WITH_CHAR (hcl, c, tt);
 		goto consumed;
 	}
+#if 0
 	else if (hb->start_c == 'b' || hb->start_c == 'B')
 	{
 		/* TODO: this part needs to be removed once 0x, 0b, 0o and etc are implemented */
@@ -2735,6 +2742,7 @@ static int flx_hmarked_bc (hcl_t* hcl, hcl_ooci_t c)
 		FEED_CONTINUE (hcl, HCL_FLX_HMARKED_NUMBER);
 		goto not_consumed;
 	}
+#endif
 	else
 	{
 		hcl_ooch_t start_c = hb->start_c;
@@ -2752,7 +2760,7 @@ not_consumed:
 
 static int flx_hmarked_binop (hcl_t* hcl, hcl_ooci_t c)
 {
-	if (hcl_is_binop_char(c))
+	if (is_binop_char(c))
 	{
 		ADD_TOKEN_CHAR(hcl, c);
 		goto consumed;
@@ -3002,7 +3010,7 @@ static int flx_binop (hcl_t* hcl, hcl_ooci_t c) /* binary operator/selector */
 	hcl_flx_binop_t* binop = FLX_BINOP(hcl);
 #endif
 
-	if (hcl_is_binop_char(c))
+	if (is_binop_char(c))
 	{
 		ADD_TOKEN_CHAR (hcl, c);
 		goto consumed;
@@ -3028,33 +3036,15 @@ static int flx_plain_number (hcl_t* hcl, hcl_ooci_t c) /* number */
 	{
 		ADD_TOKEN_CHAR (hcl, c);
 		pn->digit_count[pn->fpdec]++;
+		if (pn->tok_type == HCL_TOK_NUMLIT)
+		{
+			hcl_oow_t cand = pn->radix_cand * 10 + (c - '0');
+			if (cand < pn->radix_cand) pn->radix_cand_overflown = 1;
+			pn->radix_cand = cand;
+		}
 		goto consumed;
 	}
-	else if (c == 'x' || c == 'o' || c == 'b')
-	{
-		/* 0x12ab, 0b1010101, 0o12304567 */
-		if (!pn->fpdec && pn->digit_count[0] == 1 && pn->start_digit == '0')
-		{
-			pn->radix = (c == 'x'? 16: (c == 'o'? 8: 2));
-			ADD_TOKEN_CHAR (hcl, c);
-			pn->digit_count[0] = 0;
-			goto consumed;
-		}
-		else
-		{
-			goto non_digit_char;
-		}
-	}
-#if 0
-	else if (c == 'r')
-	{
-		/* 16r12ab, 2r1010101 */
-		if (!pn->fpdec && !pn->radix)
-		{
-		}
-	}
-#endif
-	else
+	else if (is_delim_char(c))
 	{
 		if (!pn->fpdec && c == '.')
 		{
@@ -3066,6 +3056,7 @@ static int flx_plain_number (hcl_t* hcl, hcl_ooci_t c) /* number */
 				return -1;
 			}
 			pn->fpdec = 1;
+			pn->tok_type = HCL_TOK_FPDECLIT;
 			ADD_TOKEN_CHAR (hcl, c);
 			goto consumed;
 		}
@@ -3073,7 +3064,7 @@ static int flx_plain_number (hcl_t* hcl, hcl_ooci_t c) /* number */
 		if (pn->digit_count[0] == 0)
 		{
 			hcl_setsynerrbfmt (hcl, HCL_SYNERR_NUMLIT, TOKEN_LOC(hcl), HCL_NULL,
-				"invalid numeric literal with no digit '%.*js'",
+				"invalid numeric literal with no digit after '%.*js'",
 				TOKEN_NAME_LEN(hcl), TOKEN_NAME_PTR(hcl));
 			return -1;
 		}
@@ -3085,10 +3076,74 @@ static int flx_plain_number (hcl_t* hcl, hcl_ooci_t c) /* number */
 			return -1;
 		}
 
-	non_digit_char:
-		FEED_WRAP_UP (hcl, (pn->fpdec? HCL_TOK_FPDECLIT: (pn->radix != 10? HCL_TOK_RADNUMLIT: HCL_TOK_NUMLIT)));
+		FEED_WRAP_UP (hcl, pn->tok_type);
 		goto not_consumed;
 	}
+	else
+	{
+		if (!pn->fpdec && pn->digit_count[0] == 1 && pn->start_digit == '0' && pn->tok_type == HCL_TOK_NUMLIT)
+		{
+			/* prefixed with 0 */
+			switch (c)
+			{
+				case 'x':
+					pn->tok_type = HCL_TOK_RADNUMLIT;
+					pn->radix = 16;
+					break;
+
+				case 'o':
+					pn->tok_type = HCL_TOK_RADNUMLIT;
+					pn->radix = 8;
+					break;
+
+				case 'b':
+					pn->tok_type = HCL_TOK_RADNUMLIT;
+					pn->radix = 2;
+					break;
+
+				case 'p':
+					pn->tok_type = HCL_TOK_SMPTRLIT;
+					pn->radix = 16;
+					break;
+
+				case 'e':
+					pn->tok_type = HCL_TOK_ERRLIT;
+					pn->radix = 10;
+					break;
+
+				default:
+					goto other_char;
+			}
+
+			ADD_TOKEN_CHAR (hcl, c);
+			pn->digit_count[0] = 0;
+			goto consumed;
+		}
+
+	other_char:
+		if (!pn->fpdec && pn->tok_type == HCL_TOK_NUMLIT && pn->digit_count[0] > 0 && c == 'r')
+		{
+			/* 16rABCD */
+			if (pn->radix_cand_overflown)
+			{
+				hcl_setsynerrbfmt (hcl, HCL_SYNERR_NUMLIT, TOKEN_LOC(hcl), HCL_NULL,
+					"radix too large '%.*js' before '%jc'",
+					TOKEN_NAME_LEN(hcl), TOKEN_NAME_PTR(hcl), c);
+				return -1;
+			}
+
+			pn->tok_type = HCL_TOK_RADNUMLIT;
+			pn->radix = pn->radix_cand;
+			ADD_TOKEN_CHAR (hcl, c);
+			pn->digit_count[0] = 0;
+			goto consumed;
+		}
+
+		hcl_setsynerrbfmt (hcl, HCL_SYNERR_NUMLIT, TOKEN_LOC(hcl), HCL_NULL,
+			"invalid numeric literal character '%jc' after '%.*js'",
+			c, TOKEN_NAME_LEN(hcl), TOKEN_NAME_PTR(hcl));
+		return -1;
+	}
 
 consumed:
 	return 1;
diff --git a/t/feed-01.hcl b/t/feed-01.hcl
index 5a54bf8..ec029ac 100644
--- a/t/feed-01.hcl
+++ b/t/feed-01.hcl
@@ -108,6 +108,9 @@ i := 0xAbCd93481FFAABBCCDDEeFa12837281
 j := 0o125715446440377652567463357357502240671201
 k := 0b1010101111001101100100110100100000011111111110101010101110111100110011011101111011101111101000010010100000110111001010000001
 l := 14272837210234798094990047170340811393
+m := 16rAbCd93481FFAABBCCDDEeFa12837281
+n := 36rMVV36DNKTQ0Z2Q3L027T3NGH
+o := +35r18Q4OPTU2KRS7FVR09B5MORY3
 
 if (== i j) { printf "OK: i is equal to j\n" } \
 else { printf "ERROR: i is not equal to j\n" }
@@ -115,4 +118,16 @@ if (== i k) { printf "OK: i is equal to k\n" } \
 else { printf "ERROR: i is not equal to k\n" }
 if (== i l) { printf "OK: i is equal to l\n" } \
 else { printf "ERROR: i is not equal to l\n" }
+if (== i m) { printf "OK: i is equal to m\n" } \
+else { printf "ERROR: i is not equal to m\n" }
+if (== i n) { printf "OK: i is equal to n\n" } \
+else { printf "ERROR: i is not equal to n\n" }
+if (== i o) { printf "OK: i is equal to o\n" } \
+else { printf "ERROR: i is not equal to o\n" }
+
+
+i := (- -16r123abcd128738279878172387123aabbea19849d8282882822332332 123)
+k := -1919784483373631008405784517212288102153752573650638404319957951405
+if (== i k) { printf "OK: i is %d\n" i k } \
+else { printf "ERROR: i is not equal to %d\n" k }
 }  ## END
diff --git a/t/feed-5001.err b/t/feed-5001.err
index 2020317..0037698 100644
--- a/t/feed-5001.err
+++ b/t/feed-5001.err
@@ -14,10 +14,13 @@ $include 10    ##ERROR: syntax error - $include target expected in place of '10'
 
 ---
 
-0b ##ERROR: invalid numeric literal with no digit '0b'
+0b ##ERROR: syntax error - invalid numeric literal with no digit after '0b'
 
 ---
 
+16r ##ERROR: syntax error - invalid numeric literal with no digit after '16r'
+---
+
 ##
 
 x := (+ 10 20) "aaaa"; ##ERROR: syntax error - too many rvalues
@@ -87,7 +90,28 @@ printf "[%c]\n" b'★';  ##ERROR: syntax error - wrong character literal
 
 printf "%O\n" #b[ 10 20 30 ];
 printf "%010b\n" 0b0101;
-printf "%O\n" #bxy; ##ERROR: syntax error - neither valid radixed number nor valid directive '#bxy'
+printf "%O\n" 0bxy; ##ERROR: syntax error - invalid numeric literal character 'x' after '0b'
+
+---
+
+printf "%O\n" 0b12xy ##ERROR: syntax error - invalid numeric literal character '2' after '0b1'
+
+---
+
+printf "%O\n" 0b0b11 ##ERROR: syntax error - invalid numeric literal character 'b' after '0b0'
+
+---
+
+printf "%O\n" 0o0127890 ##ERROR: syntax error - invalid numeric literal character '8' after '0o0127'
+
+---
+
+printf "%O\n"  35rabcdefghijklzabcd ##ERROR: syntax error - invalid numeric literal character 'z' after '35rabcdefghijkl'
+
+
+---
+
++ 12389127398127389217382197283197321897r11221 1 ##ERROR: syntax error - radix too large '12389127398127389217382197283197321897' before 'r'
 
 ---