diff --git a/bin/main.c b/bin/main.c
index a507038..6bbe369 100644
--- a/bin/main.c
+++ b/bin/main.c
@@ -71,7 +71,12 @@
 #	if defined(HAVE_SIGNAL_H)
 #		include <signal.h>
 #	endif
+#endif
 
+#if defined(__DOS__) || defined(_WIN32) || defined(__OS2__)
+#define FOPEN_R_FLAGS "rb"
+#else
+#define FOPEN_R_FLAGS "r"
 #endif
 
 typedef struct bb_t bb_t;
@@ -88,8 +93,8 @@ struct bb_t
 typedef struct xtn_t xtn_t;
 struct xtn_t
 {
-	const char* read_path; /* main source file */
-	const char* print_path;
+	const char* sci_path; /* main source file */
+	const char* udo_path;
 
 	int vm_running;
 	/*hcl_oop_t sym_errstr;*/
@@ -355,7 +360,7 @@ static void print_synerr (hcl_t* hcl)
 	}
 	else
 	{
-		hcl_logbfmt (hcl, HCL_LOG_STDERR, "%s", xtn->read_path);
+		hcl_logbfmt (hcl, HCL_LOG_STDERR, "%s", xtn->sci_path);
 	}
 
 	hcl_logbfmt (hcl, HCL_LOG_STDERR, "[%zu,%zu] %js",
@@ -384,7 +389,7 @@ static hcl_oop_t execute_in_interactive_mode (hcl_t* hcl)
 	retv = hcl_execute(hcl);
 
 	/* flush pending output data in the interactive mode(e.g. printf without a newline) */
-	hcl_flushio (hcl);
+	hcl_flushudio (hcl);
 
 	if (!retv)
 	{
@@ -422,7 +427,7 @@ static hcl_oop_t execute_in_batch_mode (hcl_t* hcl, int verbose)
 	/*setup_tick ();*/
 
 	retv = hcl_execute(hcl);
-	hcl_flushio (hcl);
+	hcl_flushudio (hcl);
 
 	if (!retv)
 	{
@@ -447,11 +452,25 @@ static int on_fed_cnode_in_interactive_mode (hcl_t* hcl, hcl_cnode_t* obj)
 	return 0;
 }
 
-static int feed_loop (hcl_t* hcl, xtn_t* xtn, int cflags, int verbose)
+static int feed_loop (hcl_t* hcl, xtn_t* xtn, int verbose)
 {
+	FILE* fp = HCL_NULL;
+	hcl_bch_t buf[1024];
+	hcl_oow_t xlen;
+	int is_tty;
+
+	fp = fopen(xtn->sci_path, FOPEN_R_FLAGS);
+	if (!fp)
+	{
+		hcl_logbfmt (hcl, HCL_LOG_STDERR, "ERROR: failed to open - %hs - %hs\n", xtn->sci_path, strerror(errno));
+		goto oops;
+	}
+
+	is_tty = isatty(fileno(fp));
+
 	/* override the default cnode handler. the default one simply
 	 * compiles the expression node without execution */
-	if (hcl_beginfeed(hcl, hcl_isstdreadertty(hcl)? on_fed_cnode_in_interactive_mode: HCL_NULL) <= -1)
+	if (hcl_beginfeed(hcl, is_tty? on_fed_cnode_in_interactive_mode: HCL_NULL) <= -1)
 	{
 		hcl_logbfmt (hcl, HCL_LOG_STDERR, "ERROR: cannot begin feed - [%d] %js\n", hcl_geterrnum(hcl), hcl_geterrmsg(hcl));
 		goto oops;
@@ -460,14 +479,19 @@ static int feed_loop (hcl_t* hcl, xtn_t* xtn, int cflags, int verbose)
 	/* [NOTE] it isn't a very nice idea to get this internal data and use it with read_input() */
 	while (1)
 	{
-		hcl_ooch_t* ptr;
-		hcl_oow_t xlen;
-
-		ptr = hcl_readbasesrraw(hcl, &xlen);
-		if (HCL_UNLIKELY(!ptr)) goto oops;
-		if (xlen <= 0) break;
-		if (hcl_feed(hcl, ptr, xlen) <= -1) goto feed_error;
+		xlen = fread(buf, HCL_SIZEOF(buf[0]), HCL_COUNTOF(buf), fp);
+		if (xlen > 0 && hcl_feedbchars(hcl, buf, xlen) <= -1) goto feed_error;
+		if (xlen < HCL_COUNTOF(buf))
+		{
+			if (ferror(fp))
+			{
+				hcl_logbfmt (hcl, HCL_LOG_STDERR, "ERROR: failed to read - %hs - %hs\n", xtn->sci_path, strerror(errno));
+				goto oops;
+			}
+			break;
+		}
 	}
+
 	if (hcl_endfeed(hcl) <= -1)
 	{
 	feed_error:
@@ -475,11 +499,13 @@ static int feed_loop (hcl_t* hcl, xtn_t* xtn, int cflags, int verbose)
 		else hcl_logbfmt (hcl, HCL_LOG_STDERR, "ERROR: cannot feed - [%d] %js\n", hcl_geterrnum(hcl), hcl_geterrmsg(hcl));
 		goto oops; /* TODO: proceed or just exit? */
 	}
+	fclose (fp);
 
-	if (!hcl_isstdreadertty(hcl) && hcl_getbclen(hcl) > 0) execute_in_batch_mode (hcl, verbose);
+	if (!is_tty && hcl_getbclen(hcl) > 0) execute_in_batch_mode (hcl, verbose);
 	return 0;
 
 oops:
+	if (fp) fclose (fp);
 	return -1;
 }
 
@@ -511,7 +537,6 @@ int main (int argc, char* argv[])
 
 	const char* logopt = HCL_NULL;
 	hcl_oow_t heapsize = DEFAULT_HEAPSIZE;
-	int cflags;
 	int verbose = 0;
 	int show_info = 0;
 	/*int experimental = 0;*/
@@ -640,7 +665,6 @@ int main (int argc, char* argv[])
 		return 0;
 	}
 
-
 	if (hcl_ignite(hcl, heapsize) <= -1)
 	{
 		hcl_logbfmt (hcl, HCL_LOG_STDERR, "cannot ignite hcl - [%d] %js\n", hcl_geterrnum(hcl), hcl_geterrmsg(hcl));
@@ -653,12 +677,18 @@ int main (int argc, char* argv[])
 		goto oops;
 	}
 
-	xtn->read_path = argv[opt.ind++];
-	if (opt.ind < argc) xtn->print_path = argv[opt.ind++];
-/* TODO: add scan path */
-	if (hcl_attachiostdwithbcstr(hcl, xtn->read_path, "", xtn->print_path) <= -1)
+	xtn->sci_path = argv[opt.ind++]; /* input source code file */
+	if (opt.ind < argc) xtn->udo_path = argv[opt.ind++];
+
+	if (hcl_attachsciostdwithbcstr(hcl, xtn->sci_path) <= -1)
 	{
-		hcl_logbfmt (hcl, HCL_LOG_STDERR, "ERROR: cannot attach IO streams - [%d] %js\n", hcl_geterrnum(hcl), hcl_geterrmsg(hcl));
+		hcl_logbfmt (hcl, HCL_LOG_STDERR, "ERROR: cannot attach source input stream - [%d] %js\n", hcl_geterrnum(hcl), hcl_geterrmsg(hcl));
+		goto oops;
+	}
+
+	if (hcl_attachudiostdwithbcstr(hcl, "", xtn->udo_path) <= -1) /* TODO: add udi path */
+	{
+		hcl_logbfmt (hcl, HCL_LOG_STDERR, "ERROR: cannot attach user data streams - [%d] %js\n", hcl_geterrnum(hcl), hcl_geterrmsg(hcl));
 		goto oops;
 	}
 
@@ -691,10 +721,7 @@ int main (int argc, char* argv[])
 }
 #endif
 
-	cflags = 0;
-	if (hcl_isstdreadertty(hcl)) cflags = HCL_COMPILE_CLEAR_CODE | HCL_COMPILE_CLEAR_FNBLK;
-
-	if (feed_loop(hcl, xtn, cflags, verbose) <= -1) goto oops;
+	if (feed_loop(hcl, xtn, verbose) <= -1) goto oops;
 
 	set_signal_to_default (SIGINT);
 	hcl_close (hcl);
diff --git a/go/cb.go b/go/cb.go
index b6e1a73..3b9fa7b 100644
--- a/go/cb.go
+++ b/go/cb.go
@@ -77,7 +77,7 @@ func (io *IOHandleTable) slot_to_io_handle(slot int) IOHandle {
 var io_tab IOHandleTable = IOHandleTable{}
 
 //export hcl_go_read_handler
-func hcl_go_read_handler(c *C.hcl_t, cmd C.hcl_iocmd_t, arg unsafe.Pointer) C.int {
+func hcl_go_read_handler(c *C.hcl_t, cmd C.hcl_io_cmd_t, arg unsafe.Pointer) C.int {
 	var (
 		g   *HCL
 		err error
@@ -88,13 +88,13 @@ func hcl_go_read_handler(c *C.hcl_t, cmd C.hcl_iocmd_t, arg unsafe.Pointer) C.in
 	switch cmd {
 	case C.HCL_IO_OPEN:
 		var (
-			ioarg         *C.hcl_iosrarg_t
+			ioarg         *C.hcl_io_sciarg_t
 			name          string
 			includer_name string
 			fd            int
 		)
 
-		ioarg = (*C.hcl_iosrarg_t)(arg)
+		ioarg = (*C.hcl_io_sciarg_t)(arg)
 		if ioarg.name == nil { // main stream when it's not feed based.
 			name = ""
 		} else {
@@ -119,18 +119,18 @@ func hcl_go_read_handler(c *C.hcl_t, cmd C.hcl_iocmd_t, arg unsafe.Pointer) C.in
 		return 0
 
 	case C.HCL_IO_CLOSE:
-		var ioarg *C.hcl_iosrarg_t = (*C.hcl_iosrarg_t)(arg)
+		var ioarg *C.hcl_io_sciarg_t = (*C.hcl_io_sciarg_t)(arg)
 		g.io.r.Close(int(uintptr(ioarg.handle)))
 		return 0
 
 	case C.HCL_IO_READ:
 		var (
-			ioarg *C.hcl_iosrarg_t
+			ioarg *C.hcl_io_sciarg_t
 			n     int
 			i     int
 			buf   []rune
 		)
-		ioarg = (*C.hcl_iosrarg_t)(arg)
+		ioarg = (*C.hcl_io_sciarg_t)(arg)
 
 		buf = make([]rune, 1024) // TODO:  different size...
 		n, err = g.io.r.Read(int(uintptr(ioarg.handle)), buf)
@@ -151,7 +151,7 @@ func hcl_go_read_handler(c *C.hcl_t, cmd C.hcl_iocmd_t, arg unsafe.Pointer) C.in
 }
 
 //export hcl_go_scan_handler
-func hcl_go_scan_handler(c *C.hcl_t, cmd C.hcl_iocmd_t, arg unsafe.Pointer) C.int {
+func hcl_go_scan_handler(c *C.hcl_t, cmd C.hcl_io_cmd_t, arg unsafe.Pointer) C.int {
 	var (
 		g   *HCL
 		err error
@@ -177,12 +177,12 @@ func hcl_go_scan_handler(c *C.hcl_t, cmd C.hcl_iocmd_t, arg unsafe.Pointer) C.in
 
 	case C.HCL_IO_READ:
 		var (
-			ioarg *C.hcl_ioinarg_t
+			ioarg *C.hcl_io_udiarg_t
 			n     int
 			err   error
 			buf   []rune
 		)
-		ioarg = (*C.hcl_ioinarg_t)(arg)
+		ioarg = (*C.hcl_io_udiarg_t)(arg)
 
 		buf = make([]rune, 1024) // TODO:  different size...
 		n, err = g.io.s.Read(buf)
@@ -199,7 +199,7 @@ func hcl_go_scan_handler(c *C.hcl_t, cmd C.hcl_iocmd_t, arg unsafe.Pointer) C.in
 }
 
 //export hcl_go_print_handler
-func hcl_go_print_handler(c *C.hcl_t, cmd C.hcl_iocmd_t, arg unsafe.Pointer) C.int {
+func hcl_go_print_handler(c *C.hcl_t, cmd C.hcl_io_cmd_t, arg unsafe.Pointer) C.int {
 	var (
 		g   *HCL
 		err error
@@ -225,11 +225,11 @@ func hcl_go_print_handler(c *C.hcl_t, cmd C.hcl_iocmd_t, arg unsafe.Pointer) C.i
 
 	case C.HCL_IO_WRITE:
 		var (
-			ioarg *C.hcl_iooutarg_t
+			ioarg *C.hcl_io_udoarg_t
 			data  []rune
 			err   error
 		)
-		ioarg = (*C.hcl_iooutarg_t)(arg)
+		ioarg = (*C.hcl_io_udoarg_t)(arg)
 		data = uchars_to_rune_slice((*C.hcl_uch_t)(ioarg.ptr), uintptr(ioarg.len))
 		err = g.io.p.Write(data)
 		if err != nil {
@@ -241,11 +241,11 @@ func hcl_go_print_handler(c *C.hcl_t, cmd C.hcl_iocmd_t, arg unsafe.Pointer) C.i
 
 	case C.HCL_IO_WRITE_BYTES:
 		var (
-			ioarg *C.hcl_iooutarg_t
+			ioarg *C.hcl_io_udoarg_t
 			data  []byte
 			err   error
 		)
-		ioarg = (*C.hcl_iooutarg_t)(arg)
+		ioarg = (*C.hcl_io_udoarg_t)(arg)
 		data = unsafe.Slice((*byte)(ioarg.ptr), ioarg.len)
 		err = g.io.p.WriteBytes(data)
 		if err != nil {
diff --git a/go/hcl.go b/go/hcl.go
index b06d065..9d2832c 100644
--- a/go/hcl.go
+++ b/go/hcl.go
@@ -5,17 +5,17 @@ package hcl
 #include <hcl-utl.h>
 #include <stdlib.h> // for C.freem
 
-extern int hcl_go_read_handler (hcl_t hcl, hcl_iocmd_t cmd, void* arg);
-extern int hcl_go_scan_handler (hcl_t hcl, hcl_iocmd_t cmd, void* arg);
-extern int hcl_go_print_handler (hcl_t hcl, hcl_iocmd_t cmd, void* arg);
+extern int hcl_go_read_handler (hcl_t hcl, hcl_io_cmd_t cmd, void* arg);
+extern int hcl_go_scan_handler (hcl_t hcl, hcl_io_cmd_t cmd, void* arg);
+extern int hcl_go_print_handler (hcl_t hcl, hcl_io_cmd_t cmd, void* arg);
 
-int hcl_read_handler_for_go (hcl_t hcl, hcl_iocmd_t cmd, void* arg) {
+int hcl_read_handler_for_go (hcl_t hcl, hcl_io_cmd_t cmd, void* arg) {
     return hcl_go_read_handler(hcl, cmd, arg);
 }
-int hcl_scan_handler_for_go (hcl_t hcl, hcl_iocmd_t cmd, void* arg) {
+int hcl_scan_handler_for_go (hcl_t hcl, hcl_io_cmd_t cmd, void* arg) {
     return hcl_go_scan_handler(hcl, cmd, arg);
 }
-int hcl_print_handler_for_go (hcl_t hcl, hcl_iocmd_t cmd, void* arg) {
+int hcl_print_handler_for_go (hcl_t hcl, hcl_io_cmd_t cmd, void* arg) {
     return hcl_go_print_handler(hcl, cmd, arg);
 }
 */
@@ -181,23 +181,42 @@ func (hcl *HCL) AddBuiltinPrims() error {
 	return nil
 }
 
-func (hcl *HCL) AttachIO(r IOReadImpl, s IOScanImpl, p IOPrintImpl) error {
+func (hcl *HCL) AttachSCIO(r IOReadImpl) error {
 	var x C.int
-	var io IOImplSet
+	var or IOReadImpl
 
-	io = hcl.io
+	or = hcl.io.r
 
 	hcl.io.r = r
+
+	x = C.hcl_attachscio(hcl.c, C.hcl_io_impl_t(C.hcl_read_handler_for_go))
+	if x <= -1 {
+		// restore the io handler set due to attachment failure
+		hcl.io.r = or
+		return fmt.Errorf("unable to attach source input stream handler - %s", hcl.get_errmsg())
+	}
+	return nil
+}
+
+func (hcl *HCL) AttachUDIO(s IOScanImpl, p IOPrintImpl) error {
+	var x C.int
+	var os IOScanImpl
+	var op IOPrintImpl
+
+	os = hcl.io.s
+	op = hcl.io.p
+
 	hcl.io.s = s
 	hcl.io.p = p
 
-	x = C.hcl_attachio(hcl.c,
-		C.hcl_ioimpl_t(C.hcl_read_handler_for_go),
-		C.hcl_ioimpl_t(C.hcl_scan_handler_for_go),
-		C.hcl_ioimpl_t(C.hcl_print_handler_for_go))
+	x = C.hcl_attachudio(hcl.c,
+		C.hcl_io_impl_t(C.hcl_scan_handler_for_go),
+		C.hcl_io_impl_t(C.hcl_print_handler_for_go))
 	if x <= -1 {
-		hcl.io = io // restore the io handler set due to attachment failure
-		return fmt.Errorf("unable to attach I/O handlers - %s", hcl.get_errmsg())
+		//restore the io handlers set due to attachment failure
+		hcl.io.s = os
+		hcl.io.p = op
+		return fmt.Errorf("unable to attach user data stream handlers - %s", hcl.get_errmsg())
 	}
 	return nil
 }
diff --git a/lib/hcl-s.c b/lib/hcl-s.c
index cced7c9..c0d3f05 100644
--- a/lib/hcl-s.c
+++ b/lib/hcl-s.c
@@ -718,7 +718,8 @@ hcl_server_proto_t* hcl_server_proto_open (hcl_oow_t xtnsize, hcl_server_worker_
 	if (hcl_ignite(proto->hcl, worker->server->cfg.actor_heap_size) <= -1) goto oops;
 	if (hcl_addbuiltinprims(proto->hcl) <= -1) goto oops;
 
-	if (hcl_attachio(proto->hcl, read_handler, HCL_NULL, print_handler) <= -1) goto oops;
+	if (hcl_attachscio(proto->hcl, read_handler) <= -1) goto oops;
+	if (hcl_attachudio(proto->hcl, HCL_NULL, print_handler) <= -1) goto oops;
 	return proto;
 
 oops:
diff --git a/lib/hcl.c b/lib/hcl.c
index f2ea42f..cf4146e 100644
--- a/lib/hcl.c
+++ b/lib/hcl.c
@@ -219,6 +219,10 @@ void hcl_fini (hcl_t* hcl)
 	/* deregister all callbacks */
 	while (hcl->cblist) hcl_deregcb (hcl, hcl->cblist);
 
+
+	/* detach the user data io handlers just in case */
+	hcl_detachudio (hcl);
+
 	if (hcl->sem_list)
 	{
 		hcl_freemem (hcl, hcl->sem_list);
diff --git a/lib/hcl.h b/lib/hcl.h
index 9bcc427..abe0c47 100644
--- a/lib/hcl.h
+++ b/lib/hcl.h
@@ -2240,36 +2240,54 @@ HCL_EXPORT hcl_ooch_t* hcl_readbasesrraw (
 	hcl_oow_t* xlen
 );
 
-HCL_EXPORT int hcl_attachio (
-	hcl_t*          hcl,
-	hcl_io_impl_t   sci_rdr, /* source code input handler */
-	hcl_io_impl_t   udi_rdr, /* user data input handler */
-	hcl_io_impl_t   udo_wrtr /* user data output handler */
+
+HCL_EXPORT int hcl_attachscio (
+	hcl_t*        hcl,
+	hcl_io_impl_t sci_rdr
 );
 
-HCL_EXPORT int hcl_attachiostdwithbcstr (
+HCL_EXPORT void hcl_detachscio (
+	hcl_t*        hcl
+);
+
+HCL_EXPORT int hcl_attachudio (
+	hcl_t*        hcl,
+	hcl_io_impl_t udi_rdr,
+	hcl_io_impl_t udo_wrtr
+);
+
+HCL_EXPORT void hcl_detachudio (
+	hcl_t*        hcl
+);
+
+
+HCL_EXPORT int hcl_attachsciostdwithucstr (
 	hcl_t*           hcl,
-	const hcl_bch_t* read_file,
-	const hcl_bch_t* scan_file,
-	const hcl_bch_t* print_file
+	const hcl_uch_t* sci_file
 );
 
-HCL_EXPORT int hcl_attachiostdwithucstr (
+HCL_EXPORT int hcl_attachsciostdwithbcstr (
 	hcl_t*           hcl,
-	const hcl_uch_t* read_file,
-	const hcl_uch_t* scan_file,
-	const hcl_uch_t* print_file
+	const hcl_bch_t* sci_file
 );
 
-HCL_EXPORT int hcl_isstdreadertty (
-	hcl_t*       hcl
+HCL_EXPORT int hcl_attachudiostdwithucstr (
+	hcl_t*           hcl,
+	const hcl_uch_t* udi_file,
+	const hcl_uch_t* udo_file
+);
+
+HCL_EXPORT int hcl_attachudiostdwithbcstr (
+	hcl_t*           hcl,
+	const hcl_bch_t* udi_file,
+	const hcl_bch_t* udo_file
 );
 
 HCL_EXPORT void hcl_detachio (
 	hcl_t*       hcl
 );
 
-HCL_EXPORT void hcl_flushio (
+HCL_EXPORT void hcl_flushudio (
 	hcl_t*       hcl
 );
 
diff --git a/lib/read.c b/lib/read.c
index 96a8c86..ca99df6 100644
--- a/lib/read.c
+++ b/lib/read.c
@@ -2413,7 +2413,7 @@ static int feed_from_includee (hcl_t* hcl)
 
 int hcl_beginfeed (hcl_t* hcl, hcl_on_cnode_t on_cnode)
 {
-	HCL_ASSERT (hcl, hcl->c != HCL_NULL); /* call hcl_attachio() or hcl_attachiostd() first */
+	HCL_ASSERT (hcl, hcl->c != HCL_NULL); /* call hcl_attachscio() or hcl_attachsciostd() first */
 
 	init_feed (hcl);
 	if (on_cnode) hcl->c->feed.on_cnode = on_cnode;
@@ -2732,7 +2732,7 @@ static void fini_compiler_cb (hcl_t* hcl)
 		clear_sr_names (hcl);
 		if (hcl->c->tok.name.ptr) hcl_freemem (hcl, hcl->c->tok.name.ptr);
 
-		hcl_detachio (hcl);
+		hcl_detachscio (hcl);
 
 		hcl_freemem (hcl, hcl->c);
 		hcl->c = HCL_NULL;
@@ -2786,13 +2786,11 @@ static int init_compiler (hcl_t* hcl)
 	return 0;
 }
 
-int hcl_attachio (hcl_t* hcl, hcl_io_impl_t sci_rdr, hcl_io_impl_t udi_rdr, hcl_io_impl_t udo_wrtr)
+int hcl_attachscio (hcl_t* hcl, hcl_io_impl_t sci_rdr)
 {
 	int n;
 	int inited_compiler = 0;
 	hcl_io_sciarg_t new_sciarg;
-	hcl_io_udiarg_t new_udiarg;
-	hcl_io_udoarg_t new_udoarg;
 
 	if (!hcl->c)
 	{
@@ -2800,6 +2798,7 @@ int hcl_attachio (hcl_t* hcl, hcl_io_impl_t sci_rdr, hcl_io_impl_t udi_rdr, hcl_
 		inited_compiler = 1;
 	}
 
+
 	if (sci_rdr)
 	{
 		/* The name field and the includer field are HCL_NULL
@@ -2811,34 +2810,7 @@ int hcl_attachio (hcl_t* hcl, hcl_io_impl_t sci_rdr, hcl_io_impl_t udi_rdr, hcl_
 		/* open the top-level source input stream */
 		n = sci_rdr(hcl, HCL_IO_OPEN, &new_sciarg);
 		if (n <= -1) goto oops;
-	}
 
-	if (udi_rdr)
-	{
-		HCL_MEMSET (&new_udiarg, 0, HCL_SIZEOF(new_udiarg));
-		n = udi_rdr(hcl, HCL_IO_OPEN, &new_udiarg);
-		if (n <= -1)
-		{
-			sci_rdr (hcl, HCL_IO_CLOSE, &new_sciarg);
-			goto oops;
-		}
-	}
-
-	if (udo_wrtr)
-	{
-		/* open the new output stream */
-		HCL_MEMSET (&new_udoarg, 0, HCL_SIZEOF(new_udoarg));
-		n = udo_wrtr(hcl, HCL_IO_OPEN, &new_udoarg);
-		if (n <= -1)
-		{
-			if (udi_rdr) udi_rdr (hcl, HCL_IO_CLOSE, &new_udiarg);
-			if (sci_rdr) sci_rdr (hcl, HCL_IO_CLOSE, &new_sciarg);
-			goto oops;
-		}
-	}
-
-	if (sci_rdr)
-	{
 		if (hcl->c->sci_rdr)
 		{
 			/* close the old source input stream */
@@ -2846,32 +2818,7 @@ int hcl_attachio (hcl_t* hcl, hcl_io_impl_t sci_rdr, hcl_io_impl_t udi_rdr, hcl_
 		}
 		hcl->c->sci_rdr = sci_rdr;
 		hcl->c->sci_arg = new_sciarg;
-	}
 
-	if (udi_rdr)
-	{
-		if (hcl->io.udi_rdr)
-		{
-			/* close the old input stream */
-			hcl->io.udi_rdr (hcl, HCL_IO_CLOSE, &hcl->io.udi_arg);
-		}
-		hcl->io.udi_rdr = udi_rdr;
-		hcl->io.udi_arg = new_udiarg;
-	}
-
-	if (udo_wrtr)
-	{
-		if (hcl->io.udo_wrtr)
-		{
-			/* close the old output stream */
-			hcl->io.udo_wrtr (hcl, HCL_IO_CLOSE, &hcl->io.udo_arg);
-		}
-		hcl->io.udo_wrtr = udo_wrtr;
-		hcl->io.udo_arg = new_udoarg;
-	}
-
-	if (sci_rdr)
-	{
 		/* clear unneeded source stream names */
 		/*clear_sr_names (hcl); <---- TODO: tricky to clean up here */
 
@@ -2888,12 +2835,7 @@ oops:
 	return -1;
 }
 
-void hcl_flushio (hcl_t* hcl)
-{
-	if (hcl->io.udo_wrtr) hcl->io.udo_wrtr (hcl, HCL_IO_FLUSH, &hcl->io.udo_arg);
-}
-
-void hcl_detachio (hcl_t* hcl)
+void hcl_detachscio (hcl_t* hcl)
 {
 	/* an error occurred and control has reached here
 	 * probably, some included files might not have been
@@ -2919,9 +2861,68 @@ void hcl_detachio (hcl_t* hcl)
 			hcl->c->sci_rdr (hcl, HCL_IO_CLOSE, hcl->c->curinp);
 			hcl->c->sci_rdr = HCL_NULL; /* ready for another attachment */
 		}
+	}
+}
 
+int hcl_attachudio (hcl_t* hcl, hcl_io_impl_t udi_rdr, hcl_io_impl_t udo_wrtr)
+{
+	int n;
+	hcl_io_udiarg_t new_udiarg;
+	hcl_io_udoarg_t new_udoarg;
+
+	if (udi_rdr)
+	{
+		HCL_MEMSET (&new_udiarg, 0, HCL_SIZEOF(new_udiarg));
+		n = udi_rdr(hcl, HCL_IO_OPEN, &new_udiarg);
+		if (n <= -1)
+		{
+			goto oops;
+		}
 	}
 
+	if (udo_wrtr)
+	{
+		/* open the new output stream */
+		HCL_MEMSET (&new_udoarg, 0, HCL_SIZEOF(new_udoarg));
+		n = udo_wrtr(hcl, HCL_IO_OPEN, &new_udoarg);
+		if (n <= -1)
+		{
+			if (udi_rdr) udi_rdr (hcl, HCL_IO_CLOSE, &new_udiarg);
+			goto oops;
+		}
+	}
+
+	if (udi_rdr)
+	{
+		if (hcl->io.udi_rdr)
+		{
+			/* close the old input stream */
+			hcl->io.udi_rdr (hcl, HCL_IO_CLOSE, &hcl->io.udi_arg);
+		}
+		hcl->io.udi_rdr = udi_rdr;
+		hcl->io.udi_arg = new_udiarg;
+	}
+
+	if (udo_wrtr)
+	{
+		if (hcl->io.udo_wrtr)
+		{
+			/* close the old output stream */
+			hcl->io.udo_wrtr (hcl, HCL_IO_CLOSE, &hcl->io.udo_arg);
+		}
+		hcl->io.udo_wrtr = udo_wrtr;
+		hcl->io.udo_arg = new_udoarg;
+	}
+
+	return 0;
+
+oops:
+	return -1;
+}
+
+
+void hcl_detachudio (hcl_t* hcl)
+{
 	if (hcl->io.udi_rdr)
 	{
 		hcl->io.udi_rdr (hcl, HCL_IO_CLOSE, &hcl->io.udi_arg);
@@ -2935,6 +2936,11 @@ void hcl_detachio (hcl_t* hcl)
 	}
 }
 
+void hcl_flushudio (hcl_t* hcl)
+{
+	if (hcl->io.udo_wrtr) hcl->io.udo_wrtr (hcl, HCL_IO_FLUSH, &hcl->io.udo_arg);
+}
+
 void hcl_setbasesrloc (hcl_t* hcl, hcl_oow_t line, hcl_oow_t colm)
 {
 	hcl->c->sci_arg.line = line;
diff --git a/lib/std.c b/lib/std.c
index 87813a4..fd53373 100644
--- a/lib/std.c
+++ b/lib/std.c
@@ -288,11 +288,9 @@ struct xtn_t
 	 * set these two field and reset them at the end.
 	 * since hcl_attachio() callls the open handler, these fields
 	 * are valid only inside the open handelr */
-	const char* read_path; /* main source file */
-	const char* scan_path; /* runtime input file */
-	const char* print_path; /* runtime output file */
-
-        int reader_istty;
+	const char* sci_path; /* main source file */
+	const char* udi_path; /* runtime input file */
+	const char* udo_path; /* runtime output file */
 
 	int vm_running;
 	int rcv_tick;
@@ -3241,42 +3239,38 @@ static HCL_INLINE int open_sci_stream (hcl_t* hcl, hcl_io_sciarg_t* arg)
 	#endif
 
 		bb->fp = fopen(bb->fn, FOPEN_R_FLAGS);
+		if (!bb->fp)
+		{
+			hcl_seterrbfmt (hcl, HCL_EIOERR, "unable to open %hs", bb->fn);
+			goto oops;
+		}
 	}
 	else
 	{
-		/* main stream */
+		/* main stream  */
 		hcl_oow_t pathlen;
 
-		pathlen = xtn->read_path? hcl_count_bcstr(xtn->read_path): 0;
+		pathlen = xtn->sci_path? hcl_count_bcstr(xtn->sci_path): 0;
 
 		bb = (bb_t*)hcl_callocmem(hcl, HCL_SIZEOF(*bb) + (HCL_SIZEOF(hcl_bch_t) * (pathlen + 1)));
 		if (!bb) goto oops;
 
 		bb->fn = (hcl_bch_t*)(bb + 1);
-		if (pathlen > 0 && xtn->read_path)
+		if (pathlen > 0 && xtn->sci_path)
 		{
-			hcl_copy_bcstr (bb->fn, pathlen + 1, xtn->read_path);
-			bb->fp = fopen(bb->fn, FOPEN_R_FLAGS);
+			hcl_copy_bcstr (bb->fn, pathlen + 1, xtn->sci_path);
+			/*bb->fp = fopen(bb->fn, FOPEN_R_FLAGS);*/
 		}
 		else
 		{
 			bb->fn[0] = '\0';
-			bb->fp = stdin;
+			/*bb->fp = stdin;*/
 		}
 	}
 
-	if (!bb->fp)
-	{
-		hcl_seterrbfmt (hcl, HCL_EIOERR, "unable to open %hs", bb->fn);
-		goto oops;
-	}
 
 	if (!arg->includer) /* if main stream */
 	{
-	#if defined(HAVE_ISATTY)
-		xtn->reader_istty = isatty(fileno(bb->fp));
-	#endif
-
 	/* HACK */
 		HCL_ASSERT (hcl, arg->name == HCL_NULL);
 		arg->name = hcl_dupbtooocstr(hcl, bb->fn, HCL_NULL);
@@ -3304,17 +3298,18 @@ static HCL_INLINE int close_sci_stream (hcl_t* hcl, hcl_io_sciarg_t* arg)
 	bb_t* bb;
 
 	bb = (bb_t*)arg->handle;
-	HCL_ASSERT (hcl, bb != HCL_NULL && bb->fp != HCL_NULL);
+	HCL_ASSERT (hcl, bb != HCL_NULL /*&& bb->fp != HCL_NULL*/);
 
 /* HACK */
 	if (!arg->includer && arg->name)
 	{
+		/* main stream closing */
 		hcl_freemem (hcl, arg->name);
 		arg->name = HCL_NULL;
 	}
 /* END HACK */
 
-	if (bb->fp != stdin) fclose (bb->fp);
+	if (bb->fp /*&& bb->fp != stdin*/) fclose (bb->fp);
 	hcl_freemem (hcl, bb);
 
 	arg->handle = HCL_NULL;
@@ -3403,15 +3398,15 @@ static HCL_INLINE int open_in_stream (hcl_t* hcl, hcl_io_udiarg_t* arg)
 
 	hcl_oow_t pathlen;
 
-	pathlen = xtn->read_path? hcl_count_bcstr(xtn->read_path): 0;
+	pathlen = xtn->sci_path? hcl_count_bcstr(xtn->sci_path): 0;
 
 	bb = (bb_t*)hcl_callocmem(hcl, HCL_SIZEOF(*bb) + (HCL_SIZEOF(hcl_bch_t) * (pathlen + 1)));
 	if (!bb) goto oops;
 
 	bb->fn = (hcl_bch_t*)(bb + 1);
-	if (pathlen > 0 && xtn->read_path)
+	if (pathlen > 0 && xtn->sci_path)
 	{
-		hcl_copy_bcstr (bb->fn, pathlen + 1, xtn->read_path);
+		hcl_copy_bcstr (bb->fn, pathlen + 1, xtn->sci_path);
 		bb->fp = fopen(bb->fn, FOPEN_R_FLAGS);
 	}
 	else
@@ -3503,7 +3498,7 @@ static HCL_INLINE int read_in_stream (hcl_t* hcl, hcl_io_udiarg_t* arg)
 	return 0;
 }
 
-static int scan_handler (hcl_t* hcl, hcl_io_cmd_t cmd, void* arg)
+static int udi_handler (hcl_t* hcl, hcl_io_cmd_t cmd, void* arg)
 {
 	switch (cmd)
 	{
@@ -3538,11 +3533,11 @@ static HCL_INLINE int open_out_stream (hcl_t* hcl, hcl_io_udoarg_t* arg)
 #define FOPEN_W_FLAGS "w"
 #endif
 
-	fp = (xtn->print_path && xtn->print_path[0] != '\0'? fopen(xtn->print_path, FOPEN_W_FLAGS): stdout);
+	fp = (xtn->udo_path && xtn->udo_path[0] != '\0'? fopen(xtn->udo_path, FOPEN_W_FLAGS): stdout);
 	if (!fp)
 	{
-		if (xtn->print_path)
-			hcl_seterrbfmt (hcl, HCL_EIOERR, "unable to open %hs", xtn->print_path);
+		if (xtn->udo_path)
+			hcl_seterrbfmt (hcl, HCL_EIOERR, "unable to open %hs", xtn->udo_path);
 		else
 			hcl_seterrnum (hcl, HCL_EIOERR);
 		return -1;
@@ -3632,7 +3627,7 @@ static HCL_INLINE int flush_out_stream (hcl_t* hcl, hcl_io_udoarg_t* arg)
 	return 0;
 }
 
-static int print_handler (hcl_t* hcl, hcl_io_cmd_t cmd, void* arg)
+static int udo_handler (hcl_t* hcl, hcl_io_cmd_t cmd, void* arg)
 {
 	switch (cmd)
 	{
@@ -3659,73 +3654,96 @@ static int print_handler (hcl_t* hcl, hcl_io_cmd_t cmd, void* arg)
 
 /* --------------------------------------------------------------------- */
 
-int hcl_attachiostdwithbcstr (hcl_t* hcl, const hcl_bch_t* read_file, const hcl_bch_t* scan_file, const hcl_bch_t* print_file)
+int hcl_attachsciostdwithbcstr (hcl_t* hcl, const hcl_bch_t* sci_file)
 {
 	xtn_t* xtn = GET_XTN(hcl);
 	int n;
 
-	HCL_ASSERT (hcl, xtn->read_path == HCL_NULL);
-	HCL_ASSERT (hcl, xtn->scan_path == HCL_NULL);
-	HCL_ASSERT (hcl, xtn->print_path == HCL_NULL);
+	HCL_ASSERT (hcl, xtn->sci_path == HCL_NULL);
+	
+	xtn->sci_path = sci_file;
 
-	xtn->read_path = read_file;
-	xtn->scan_path = scan_file;
-	xtn->print_path = print_file;
+	n = hcl_attachscio(hcl, sci_handler);
 
-	n = hcl_attachio(hcl, sci_handler, scan_handler, print_handler);
-
-	xtn->read_path = HCL_NULL;
-	xtn->scan_path = HCL_NULL;
-	xtn->print_path = HCL_NULL;
+	xtn->sci_path = HCL_NULL;
 
 	return n;
 }
 
-int hcl_attachiostdwithucstr (hcl_t* hcl, const hcl_uch_t* read_file, const hcl_uch_t* scan_file, const hcl_uch_t* print_file)
+int hcl_attachsciostdwithucstr (hcl_t* hcl, const hcl_uch_t* sci_file)
 {
 	xtn_t* xtn = GET_XTN(hcl);
 	int n;
 
-	HCL_ASSERT (hcl, xtn->read_path == HCL_NULL);
-	HCL_ASSERT (hcl, xtn->scan_path == HCL_NULL);
-	HCL_ASSERT (hcl, xtn->print_path == HCL_NULL);
+	HCL_ASSERT (hcl, xtn->sci_path == HCL_NULL);
 
-	xtn->read_path = hcl_duputobcstr(hcl, read_file, HCL_NULL);
-	if (HCL_UNLIKELY(!xtn->read_path)) return -1;
+	xtn->sci_path = hcl_duputobcstr(hcl, sci_file, HCL_NULL);
+	if (HCL_UNLIKELY(!xtn->sci_path)) return -1;
+	
+	n = hcl_attachscio(hcl, sci_handler);
 
-	xtn->scan_path = hcl_duputobcstr(hcl, scan_file, HCL_NULL);
-	if (HCL_UNLIKELY(!xtn->scan_path))
-	{
-		hcl_freemem (hcl, (void*)xtn->read_path);
-		xtn->read_path = HCL_NULL;
-		return -1;
-	}
-
-	xtn->print_path = hcl_duputobcstr(hcl, print_file, HCL_NULL);
-	if (HCL_UNLIKELY(!xtn->print_path))
-	{
-		hcl_freemem (hcl, (void*)xtn->scan_path);
-		hcl_freemem (hcl, (void*)xtn->read_path);
-		xtn->scan_path = HCL_NULL;
-		xtn->read_path = HCL_NULL;
-		return -1;
-	}
-
-	n = hcl_attachio(hcl, sci_handler, scan_handler, print_handler);
-
-	hcl_freemem (hcl, (void*)xtn->read_path);
-	hcl_freemem (hcl, (void*)xtn->scan_path);
-	hcl_freemem (hcl, (void*)xtn->print_path);
-
-	xtn->read_path = HCL_NULL;
-	xtn->scan_path = HCL_NULL;
-	xtn->print_path = HCL_NULL;
+	hcl_freemem (hcl, (void*)xtn->sci_path);	
+	xtn->sci_path = HCL_NULL;
 
 	return n;
 }
 
-int hcl_isstdreadertty (hcl_t* hcl)
+/* --------------------------------------------------------------------- */
+
+int hcl_attachudiostdwithbcstr (hcl_t* hcl, const hcl_bch_t* udi_file, const hcl_bch_t* udo_file)
 {
 	xtn_t* xtn = GET_XTN(hcl);
-	return xtn->reader_istty;
+	int n;
+
+	HCL_ASSERT (hcl, xtn->udi_path == HCL_NULL);
+	HCL_ASSERT (hcl, xtn->udo_path == HCL_NULL);
+
+
+	xtn->udi_path = udi_file;
+	xtn->udo_path = udo_file;
+
+	n = hcl_attachudio(hcl, udi_handler, udo_handler);
+
+
+	xtn->udi_path = HCL_NULL;
+	xtn->udo_path = HCL_NULL;
+
+	return n;
 }
+
+int hcl_attachudiostdwithucstr (hcl_t* hcl, const hcl_uch_t* udi_file, const hcl_uch_t* udo_file)
+{
+	xtn_t* xtn = GET_XTN(hcl);
+	int n;
+
+	HCL_ASSERT (hcl, xtn->udi_path == HCL_NULL);
+	HCL_ASSERT (hcl, xtn->udo_path == HCL_NULL);
+
+
+	xtn->udi_path = hcl_duputobcstr(hcl, udi_file, HCL_NULL);
+	if (HCL_UNLIKELY(!xtn->udi_path))
+	{
+		hcl_freemem (hcl, (void*)xtn->sci_path);
+		return -1;
+	}
+
+	xtn->udo_path = hcl_duputobcstr(hcl, udo_file, HCL_NULL);
+	if (HCL_UNLIKELY(!xtn->udo_path))
+	{
+		hcl_freemem (hcl, (void*)xtn->udi_path);
+		xtn->udi_path = HCL_NULL;
+		return -1;
+	}
+
+	n = hcl_attachudio(hcl, udi_handler, udo_handler);
+
+	hcl_freemem (hcl, (void*)xtn->udi_path);
+	hcl_freemem (hcl, (void*)xtn->udo_path);
+
+	xtn->udi_path = HCL_NULL;
+	xtn->udo_path = HCL_NULL;
+
+	return n;
+}
+
+
diff --git a/main.go b/main.go
index 9ae0d5d..60d2df5 100644
--- a/main.go
+++ b/main.go
@@ -87,7 +87,13 @@ func main() {
 		goto oops
 	}
 
-	err = x.AttachIO(&rfh, &sfh, &pfh)
+	err = x.AttachSCIO(&rfh)
+	if err != nil {
+		fmt.Printf("Error: %s\n", err.Error())
+		goto oops
+	}
+
+	err = x.AttachUDIO(&sfh, &pfh)
 	if err != nil {
 		fmt.Printf("Error: %s\n", err.Error())
 		goto oops