diff --git a/Makefile.am b/Makefile.am
index 2add1bc..ade16c2 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -45,7 +45,7 @@ hclgo_LINK = mv -f hclgo.bin hclgo$(EXEEXT) || echo "FAILED TO LINK"
 hclgo.bin:
 	cp -pf $(srcdir)/go.mod $(builddir)/go.mod >/dev/null 2>&1 || true
 	chmod u+w $(builddir)/go.mod ## with `make distcheck`, the echo's redirection to the file fails without this permission change
-	sed -ri "/^[[:space:]]*replace[[:space:]]+cfg[[:space:]]*=>/d" $(builddir)/go.mod
+	sed -r -i -e "/^[[:space:]]*replace[[:space:]]+cfg[[:space:]]*=>/d" $(builddir)/go.mod
 	echo -e "\nreplace cfg => $(abs_builddir)/go/cfg" >> $(builddir)/go.mod
 	[ -f $(srcdir)/go.sum ] && cp -pf $(srcdir)/go.sum $(builddir)/go.sum >/dev/null 2>&1 || true
 	CGO_CFLAGS="-I$(abs_srcdir)/lib -I$(abs_builddir)/lib $(CFLAGS)" \
diff --git a/Makefile.in b/Makefile.in
index 1dc7c95..ff91cdb 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -940,7 +940,7 @@ clean-local:
 @ENABLE_HCLGO_TRUE@hclgo.bin:
 @ENABLE_HCLGO_TRUE@	cp -pf $(srcdir)/go.mod $(builddir)/go.mod >/dev/null 2>&1 || true
 @ENABLE_HCLGO_TRUE@	chmod u+w $(builddir)/go.mod ## with `make distcheck`, the echo's redirection to the file fails without this permission change
-@ENABLE_HCLGO_TRUE@	sed -ri "/^[[:space:]]*replace[[:space:]]+cfg[[:space:]]*=>/d" $(builddir)/go.mod
+@ENABLE_HCLGO_TRUE@	sed -r -i -e "/^[[:space:]]*replace[[:space:]]+cfg[[:space:]]*=>/d" $(builddir)/go.mod
 @ENABLE_HCLGO_TRUE@	echo -e "\nreplace cfg => $(abs_builddir)/go/cfg" >> $(builddir)/go.mod
 @ENABLE_HCLGO_TRUE@	[ -f $(srcdir)/go.sum ] && cp -pf $(srcdir)/go.sum $(builddir)/go.sum >/dev/null 2>&1 || true
 @ENABLE_HCLGO_TRUE@	CGO_CFLAGS="-I$(abs_srcdir)/lib -I$(abs_builddir)/lib $(CFLAGS)" \
diff --git a/go/cb.go b/go/cb.go
index 968ba86..10bdb86 100644
--- a/go/cb.go
+++ b/go/cb.go
@@ -9,7 +9,11 @@ import "C"
 import (
 	//	"bufio"
 	//	"io"
+	"bufio"
+	"io"
 	"os"
+	"sync"
+	"unsafe"
 	// "sync"
 	// "unsafe"
 )
@@ -19,7 +23,6 @@ type IOHandle struct {
 	ioif interface{}
 }
 
-/*
 type IOHandleTable struct {
 	mtx        sync.Mutex
 	handles    []IOHandle
@@ -348,10 +351,10 @@ func (p *ScanFileHandler) Open(g *HCL) error {
 	)
 
 	f = os.Stdin
-		//f, err = os.Open("/dev/stdin")
-		//if err != nil {
-		//	return err
-		//}
+	//f, err = os.Open("/dev/stdin")
+	//if err != nil {
+	//	return err
+	//}
 
 	p.r = bufio.NewReader(f)
 	p.f = f
@@ -407,10 +410,10 @@ func (p *PrintFileHandler) Open(g *HCL) error {
 	//	err error
 	)
 
-//		f, err = os.OpenFile("/dev/stdout", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
-//		if err != nil {
-//			return err
-//		}
+	//		f, err = os.OpenFile("/dev/stdout", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
+	//		if err != nil {
+	//			return err
+	//		}
 
 	f = os.Stdout
 
@@ -455,4 +458,3 @@ func (p *PrintFileHandler) Flush() error {
 	//fmt.Fprintf(os.Stderr, "XXXXXXXXXX flush porint\n")
 	return p.w.Flush()
 }
-*/
diff --git a/go/hcl.go b/go/hcl.go
index e98741d..924cd0f 100644
--- a/go/hcl.go
+++ b/go/hcl.go
@@ -12,13 +12,23 @@ import (
 	"unsafe"
 )
 
+type IOImpl interface {
+	Open(g *HCL, name string, includer_name string) (int, error)
+	Close(fd int)
+	Read(fd int, buf []rune) (int, error)
+	Write(data []rune) error
+	WriteBytes(data []byte) error
+	Flush() error
+}
+
 type HCL struct {
 	c       *C.hcl_t
 	inst_no int
 
 	io struct {
-		r IOHandle
-		w IOHandle
+		r IOImpl
+		s IOImpl
+		p IOImpl
 	}
 }
 
@@ -82,7 +92,14 @@ func (hcl *HCL) AddBuiltinPrims() error {
 	return nil
 }
 
-func (hcl *HCL) AttachIO() error {
+func (hcl *HCL) AttachIO(r IOImpl, w IOImpl, p IOImpl) error {
+	hcl.io.r = r
+	hcl.io.s = s
+	hcl.io.p = p
+	if C.hcl_attachio(hcl.c, go_read_handler, go_scan_handler, go_print_handler) <= -1 {
+		// TODO: restore to the old value..
+		return fmt.Errorf("unable to attach I/O handlers: %s", string(ucstr_to_rune_slice(C.hcl_geterrstr(hcl.c))))
+	}
 	return nil
 }
 
diff --git a/main.go b/main.go
index a1dafb2..85e97dd 100644
--- a/main.go
+++ b/main.go
@@ -29,10 +29,11 @@ int print_handler (hcl_t* hcl, hcl_iocmd_t cmd, void* arg)
 //import "C"
 
 import (
-	"fmt"
-	hcl "code.miflux.com/hyung-hwan/hcl/go"
-	"os"
 	_ "cfg"
+	"fmt"
+	"os"
+
+	hcl "code.miflux.com/hyung-hwan/hcl/go"
 )
 
 /*
@@ -105,11 +106,9 @@ func main() {
 	var x *hcl.HCL = nil
 	var err error = nil
 
-	/*
-		var rfh hcl.ReadFileHandler
-		var sfh hcl.ScanFileHandler
-		var pfh hcl.PrintFileHandler
-	*/
+	var rfh hcl.ReadFileHandler
+	var sfh hcl.ScanFileHandler
+	var pfh hcl.PrintFileHandler
 
 	x, err = hcl.New()
 	if err != nil {
@@ -127,21 +126,18 @@ func main() {
 		goto oops
 	}
 
-	/*
-	   	err = x.AttachIO(&rfh, &sfh, &pfh)
-	   	if err != nil {
-	   		fmt.Printf("Error - %s", err.Error())
-	   	}
-	   	x.FeedString(`(printf ">>>>>>>>> [%d]\n" (+ 30 455))
-
+	err = x.AttachIO(rfh, sfh, pfh)
+	if err != nil {
+		fmt.Printf("Error - %s", err.Error())
+	}
+	x.FeedString(`(printf ">>>>>>>>> [%d]\n" (+ 30 455))
 	   (printf ">>>>>>>>> [%d]\n" (+ 11 455))
 	   #include "a.hcl"
 	   (printf ">>>>>>>>> [%d]\n" (+ 20 455))`)
 
-	   	x.EndFeed()
-	   	x.Execute()
+	x.EndFeed()
+	x.Execute()
 
-	*/
 	x.Close()
 
 	os.Exit(0)