func MakeIface(itab lisp.Object, data lisp.Object) *Iface {
	return &Iface{itab: itab, data: data}
}
MakeIface returns interface value for given data object.
Dynamic type is updated accordingly.
package rt
import (
	"emacs/lisp"
)
func itabTag(itab lisp.Object) lisp.Object {
	return aref(itab, 0)
}
func itabMethod(itab lisp.Object, n int) lisp.Object {
	return aref(itab, n+1)
}
type Iface struct {
	itab lisp.Object
	data lisp.Object
}