diff --git a/lib/comp.c b/lib/comp.c
index 1d5b8fd..2687371 100644
--- a/lib/comp.c
+++ b/lib/comp.c
@@ -2614,7 +2614,9 @@ static int compile_class (hcl_t* hcl, hcl_cnode_t* src, int defclass)
 
 	if (class_name)
 	{
-		//SWITCH_TOP_CFRAME (hcl, COP_COMPILE_SYMBOL_LITERAL, class_name); /* 1 - push the class name for a named class */
+	#if 0
+		SWITCH_TOP_CFRAME (hcl, COP_COMPILE_SYMBOL_LITERAL, class_name); /* 1 - push the class name for a named class */
+	#else
 		hcl_oow_t index;
 		hcl_oop_t cons, sym;
 
@@ -2628,8 +2630,12 @@ static int compile_class (hcl_t* hcl, hcl_cnode_t* src, int defclass)
 			if (HCL_UNLIKELY(!cons)) return -1;
 		}
 
-		if (add_literal(hcl, cons, &index) <= -1) return -1;
-		if (emit_single_param_instruction(hcl, HCL_CODE_PUSH_LITERAL_0, index, HCL_CNODE_GET_LOC(class_name)) <= -1) return -1;
+		/* add an association in the system dictionary to the literal frame.
+		 * this provides performance advantage at the execution time because
+		 * the dictionary doesn't need to be searched for the object.  */
+		if (add_literal(hcl, cons, &index) <= -1 ||
+		    emit_single_param_instruction(hcl, HCL_CODE_PUSH_LITERAL_0, index, HCL_CNODE_GET_LOC(class_name)) <= -1) return -1;
+	#endif
 	}
 	else
 	{
diff --git a/lib/read.c b/lib/read.c
index ecd5052..2ce16e7 100644
--- a/lib/read.c
+++ b/lib/read.c
@@ -1871,6 +1871,7 @@ static int feed_process_token (hcl_t* hcl)
 			hcl_oow_t i;
 			hcl_oow_t v = 0;
 
+			/* 0pNNNN */
 			HCL_ASSERT (hcl, TOKEN_NAME_LEN(hcl) >= 3);
 			for (i = 2; i < TOKEN_NAME_LEN(hcl); i++)
 			{
diff --git a/lib/x-client.c b/lib/x-client.c
index f4f2951..9b345fc 100644
--- a/lib/x-client.c
+++ b/lib/x-client.c
@@ -735,7 +735,7 @@ hcl_client_logbfmt(client, HCL_LOG_STDERR, "local in read error - %hs\n", strerr
 	}
 	else if (n == 0)
 	{
-hcl_client_logbfmt(client, HCL_LOG_STDERR, "local in eof\n");
+/*hcl_client_logbfmt(client, HCL_LOG_STDERR, "local in eof\n");*/
 /* TODO ARRANGE TO FINISH.. AFTER EXUCTION OF REMAINING STUFF... */
 		//client->stopreq = 1;
 		client->state |= STATE_LOCAL_IN_CLOSED;
@@ -747,7 +747,7 @@ hcl_client_logbfmt(client, HCL_LOG_STDERR, "local to remote  (execute)- %hs\n",
 	}
 	else
 	{
-hcl_client_logbfmt(client, HCL_LOG_STDERR, "local read - %ld\n", (long)n);
+/*hcl_client_logbfmt(client, HCL_LOG_STDERR, "local read - %ld\n", (long)n);*/
 		n = client_send_to_remote(client, HCL_XPKT_CODE, buf, n);
 		if (n <= -1)
 		{
diff --git a/lib/x-server.c b/lib/x-server.c
index d10974c..dfed0b2 100644
--- a/lib/x-server.c
+++ b/lib/x-server.c
@@ -547,7 +547,7 @@ printf ("IO CLOSE SOMETHING...........\n");
 			worker_hcl_xtn_t* xtn = (worker_hcl_xtn_t*)hcl_getxtn(hcl);
 			hcl_io_udoarg_t* outarg = (hcl_io_udoarg_t*)arg;
 
-printf ("IO WRITE SOMETHING...........\n");
+/*printf ("IO WRITE SOMETHING...........\n");*/
 			if (send_chars(xtn->worker->proto, HCL_XPKT_STDOUT, outarg->ptr, outarg->len) <= -1)
 			{
 				/* TODO: change error code and message. propagage the errormessage from proto */
@@ -567,7 +567,7 @@ printf ("IO WRITE SOMETHING...........\n");
 			worker_hcl_xtn_t* xtn = (worker_hcl_xtn_t*)hcl_getxtn(hcl);
 			hcl_io_udoarg_t* outarg = (hcl_io_udoarg_t*)arg;
 
-printf ("IO WRITE SOMETHING BYTES...........\n");
+/*printf ("IO WRITE SOMETHING BYTES...........\n");*/
 			if (send_bytes(xtn->worker->proto, HCL_XPKT_STDOUT, outarg->ptr, outarg->len) <= -1)
 			{
 				/* TODO: change error code and message. propagage the errormessage from proto */
@@ -1037,7 +1037,7 @@ static int send_bytes (hcl_xproto_t* proto, hcl_xpkt_type_t xpkt_type, const hcl
 	ptr = cur = data;
 	end = data + len;
 
-printf ("SENDING BYTES [%.*s]\n", (int)len, data);
+/*printf ("SENDING BYTES [%.*s]\n", (int)len, data);*/
 	do
 	{
 		int nv;
diff --git a/lib/xchg.c b/lib/xchg.c
index ce56d83..f500ce9 100644
--- a/lib/xchg.c
+++ b/lib/xchg.c
@@ -43,6 +43,8 @@ enum hcl_xchg_type_t
 	/* literals */
 	HCL_XCHG_STRING_U,
 	HCL_XCHG_STRING_B,
+	HCL_XCHG_SYMLIT_U, /* literal symbol */
+	HCL_XCHG_SYMLIT_B, /* literal symbol */
 	HCL_XCHG_SYMBOL_U, /* contained in a cons cell */
 	HCL_XCHG_SYMBOL_B, /* contained in a cons cell */
 	HCL_XCHG_SMOOI,
@@ -186,6 +188,7 @@ int hcl_marshalcode (hcl_t* hcl, const hcl_code_t* code, hcl_xchg_writer_t wrtr,
 			}
 
 			case HCL_BRAND_STRING:
+			case HCL_BRAND_SYMBOL:
 			{
 			#if defined(HCL_OOCH_IS_UCH)
 				hcl_uch_t* ucsptr;
@@ -195,7 +198,7 @@ int hcl_marshalcode (hcl_t* hcl, const hcl_code_t* code, hcl_xchg_writer_t wrtr,
 				int n;
 
 				/* write 1-byte brand */
-				b = (hcl_uint8_t)HCL_XCHG_STRING_U;
+				b = (hcl_uint8_t)(brand == HCL_BRAND_STRING? HCL_XCHG_STRING_U: HCL_XCHG_SYMLIT_U);
 				if (wrtr(hcl, &b, HCL_SIZEOF(b), ctx) <= -1) goto oops;
 
 			string_body:
@@ -224,7 +227,6 @@ int hcl_marshalcode (hcl_t* hcl, const hcl_code_t* code, hcl_xchg_writer_t wrtr,
 				}
 			#else
 				/* write 1-byte brand */
-				b = (hcl_uint8_t)HCL_XCHG_BSTRING;
 				if (wrtr(hcl, &b, HCL_SIZEOF(b), ctx) <= -1) goto oops;
 
 			string_body:
@@ -265,6 +267,9 @@ int hcl_unmarshalcode (hcl_t* hcl, hcl_code_t* code, hcl_xchg_reader_t rdr, void
 	hcl_uint8_t b;
 	hcl_oow_t w;
 
+	hcl_uch_t* usym_buf = HCL_NULL;
+	hcl_oow_t usym_buf_capa = 0;
+
 	/* [NOTE]
 	 *  this function may pollute the code data when it fails because it doesn't
 	 *  roll back changed made to the memory pointed to by 'code'. the caller side
@@ -345,9 +350,11 @@ int hcl_unmarshalcode (hcl_t* hcl, hcl_code_t* code, hcl_xchg_reader_t rdr, void
 			}
 
 			case HCL_XCHG_STRING_U:
+			case HCL_XCHG_SYMLIT_U:
 			case HCL_XCHG_SYMBOL_U:
 			{
 				hcl_bch_t bcsbuf[64];
+				hcl_uch_t* ucsptr;
 				hcl_oow_t bcslen, bcsres, ucslen, ucspos;
 				hcl_oow_t nbytes, nchars;
 				hcl_oop_t ns;
@@ -368,8 +375,22 @@ int hcl_unmarshalcode (hcl_t* hcl, hcl_code_t* code, hcl_xchg_reader_t rdr, void
 				}
 				nbytes = hcl_leoowtoh(w);
 
-				ns = hcl_makestring(hcl, HCL_NULL, nchars);
-				if (HCL_UNLIKELY(!ns)) goto oops;
+				if (b == HCL_XCHG_STRING_U)
+				{
+					ns = hcl_makestring(hcl, HCL_NULL, nchars);
+					if (HCL_UNLIKELY(!ns)) goto oops;
+					ucsptr = HCL_OBJ_GET_CHAR_PTR(ns, 0);
+				}
+				else
+				{
+					if (nchars > usym_buf_capa)
+					{
+						usym_buf_capa = nchars * HCL_SIZEOF(usym_buf[0]);
+						usym_buf = (hcl_uch_t*)hcl_allocmem(hcl, usym_buf_capa);
+						if (HCL_UNLIKELY(!usym_buf)) goto oops;
+					}
+					ucsptr = usym_buf;
+				}
 
 				ucspos = 0;
 				bcsres = 0;
@@ -386,7 +407,7 @@ int hcl_unmarshalcode (hcl_t* hcl, hcl_code_t* code, hcl_xchg_reader_t rdr, void
 					HCL_ASSERT(hcl, ucspos < nchars);
 					bcsres = bcslen;
 					ucslen = nchars - ucspos;
-					if (hcl_convbtouchars(hcl, bcsbuf, &bcslen, HCL_OBJ_GET_CHAR_PTR(ns, ucspos), &ucslen) <= -1 && bcslen <= 0)
+					if (hcl_convbtouchars(hcl, bcsbuf, &bcslen, &ucsptr[ucspos], &ucslen) <= -1 && bcslen <= 0)
 					{
 						goto oops;
 					}
@@ -399,14 +420,21 @@ int hcl_unmarshalcode (hcl_t* hcl, hcl_code_t* code, hcl_xchg_reader_t rdr, void
 
 				HCL_ASSERT(hcl, ucspos == nchars);
 
-				if (b == HCL_XCHG_SYMBOL_U)
+				if (b != HCL_XCHG_STRING_U)
 				{
+					ns = hcl_makesymbol(hcl, usym_buf, nchars);
+					if (HCL_UNLIKELY(!ns)) goto oops;
+
+					if (b == HCL_XCHG_SYMBOL_U)
+					{
 					/* form a cons cell */
-					hcl_oop_t nc;
-					hcl_pushvolat(hcl, &ns);
-					nc = hcl_makecons(hcl, ns, hcl->_nil);
-					hcl_popvolat(hcl);
-					ns = nc;
+						hcl_oop_t nc;
+						hcl_pushvolat(hcl, &ns);
+						nc = hcl_makecons(hcl, ns, hcl->_nil);
+						hcl_popvolat(hcl);
+						if (HCL_UNLIKELY(!nc)) goto oops;
+						ns = nc;
+					}
 				}
 
 				if (hcl_addliteraltocode(hcl, code, ns, 0, HCL_NULL) <= -1) goto oops;
@@ -533,6 +561,7 @@ int hcl_unmarshalcode (hcl_t* hcl, hcl_code_t* code, hcl_xchg_reader_t rdr, void
 	return 0;
 
 oops:
+	if (usym_buf) hcl_freemem (hcl, usym_buf);
 	return -1;
 }
 /* -------------------------------------------------------------------- */
@@ -609,7 +638,12 @@ int hcl_brewcode (hcl_t* hcl, hcl_code_t* code)
 	if (!code->bc.ptr)
 	{
 		code->bc.ptr = (hcl_oob_t*)hcl_allocmem(hcl, HCL_SIZEOF(*code->bc.ptr) * HCL_BC_BUFFER_INIT); /* TODO: set a proper intial size */
-		if (HCL_UNLIKELY(!code->bc.ptr)) return -1;
+		if (HCL_UNLIKELY(!code->bc.ptr))
+		{
+			const hcl_ooch_t* orgmsg = hcl_backuperrmsg(hcl);
+			hcl_seterrbfmt (hcl, HCL_ERRNUM(hcl), "unable to allocate code buffer - %js", orgmsg);
+			return -1;
+		}
 		HCL_ASSERT (hcl, code->bc.len == 0);
 		code->bc.capa = HCL_BC_BUFFER_INIT;
 	}
@@ -619,11 +653,15 @@ int hcl_brewcode (hcl_t* hcl, hcl_code_t* code)
 		code->dbgi = (hcl_dbgi_t*)hcl_allocmem(hcl, HCL_SIZEOF(*code->dbgi) * HCL_BC_BUFFER_INIT);
 		if (HCL_UNLIKELY(!code->dbgi))
 		{
+			const hcl_ooch_t* orgmsg = hcl_backuperrmsg(hcl);
+			hcl_seterrbfmt (hcl, HCL_ERRNUM(hcl), "unable to allocate debug info buffer - %js", orgmsg);
+
 			/* bc.ptr and dbgi go together. so free bc.ptr if dbgi allocation fails */
 			hcl_freemem (hcl, code->bc.ptr);
 			code->bc.ptr = HCL_NULL;
 			code->bc.len = 0;
 			code->bc.capa = 0;
+
 			return -1;
 		}
 
@@ -634,7 +672,12 @@ int hcl_brewcode (hcl_t* hcl, hcl_code_t* code)
         if (!code->lit.arr)
         {
                 code->lit.arr = (hcl_oop_oop_t)hcl_makengcarray(hcl, HCL_LIT_BUFFER_INIT); /* TOOD: set a proper initial size */
-                if (HCL_UNLIKELY(!code->lit.arr)) return -1;
+                if (HCL_UNLIKELY(!code->lit.arr))
+		{
+			const hcl_ooch_t* orgmsg = hcl_backuperrmsg(hcl);
+			hcl_seterrbfmt (hcl, HCL_ERRNUM(hcl), "unable to allocate literal frame - %js", orgmsg);
+			return -1;
+		}
                 HCL_ASSERT (hcl, code->lit.len == 0);
         }
 
@@ -699,7 +742,12 @@ int hcl_addliteraltocode (hcl_t* hcl, hcl_code_t* code, hcl_oop_t obj, hcl_oow_t
 
 		newcapa = HCL_ALIGN(capa + 1, HCL_LIT_BUFFER_ALIGN);
 		tmp = hcl_remakengcarray(hcl, (hcl_oop_t)code->lit.arr, newcapa);
-		if (HCL_UNLIKELY(!tmp)) return -1;
+		if (HCL_UNLIKELY(!tmp))
+		{
+			const hcl_ooch_t* orgmsg = hcl_backuperrmsg(hcl);
+			hcl_seterrbfmt (hcl, HCL_ERRNUM(hcl), "unable to resize literal frame - %js", orgmsg);
+			return -1;
+		}
 
 		code->lit.arr = (hcl_oop_oop_t)tmp;
 	}
@@ -707,7 +755,9 @@ int hcl_addliteraltocode (hcl_t* hcl, hcl_code_t* code, hcl_oop_t obj, hcl_oow_t
 	if (index) *index = code->lit.len - lfbase;
 
 	((hcl_oop_oop_t)code->lit.arr)->slot[code->lit.len++] = obj;
-	/* TODO: RDONLY? */
-	/*if (HCL_IS_OOP_POINTER(obj)) HCL_OBJ_SET_FLAGS_RDONLY(obj, 1); */
+	/* make read-only an object in the literal table.
+	 * some immutable objects(e.g. literal symbol) don't need this part
+	 * but we just execute it regardless */
+	if (HCL_OOP_IS_POINTER(obj)) HCL_OBJ_SET_FLAGS_RDONLY (obj, 1);
 	return 0;
 }
diff --git a/t/call-5001.err b/t/call-5001.err
index 2814e5f..6229ee1 100644
--- a/t/call-5001.err
+++ b/t/call-5001.err
@@ -95,3 +95,13 @@ try { throw "1111"; } catch (e) {
 fun a:get_999() { ##ERROR: exception not handled - "a accessed without initialization"
 	return  999;
 }
+
+---
+
+k := (core.basicAt "abcdefg" 1)
+core.basicAtPut "xbcdefghiklmnl" 4 k ##ERROR: exception not handled - "receiver immutable - \"xbcdefghiklmnl\""
+
+---
+
+k := (core.basicAt #abcdefg 1)
+core.basicAtPut #xbcdefghiklmnl 4 k ##ERROR: exception not handled - "receiver immutable - #xbcdefghiklmnl"