[Xotcl] namespace in constructor referring an instvar?

[Tuyen Hoang]

Can  anyone tell me how to refer an instvar from within a namespace defined 
inside a  class constructor? With my attempt below the $iss in the tk_messageBox 
line is  undefined.
 
Class  create MatlabInterface
 
MatlabInterface  instproc init {} {
     my instvar iss
     namespace eval MicWatch {
         proc add {} {
             tk_messageBox -type ok -icon info -title "MicWatch" -message  
"$iss"
         }
     }
}
 
I’m new  to Tcl, let alone XOTcl, and don’t know how to search the posts in the 
mailing  list so forgive me if the question has been asked before.
 
Regards,
 
Tuyen