Linking reactive software to the X-Window System

We discuss our experience with linking (existing) reactive applications to X11 based graphical user interfaces. For implementing the user interface we choose to use the Tcl/Tk toolkit, whereas the application itself may be written in any language (even a declarative one) that provides means to perform primitive I/O. The application and the graphical user interface run as separate processes and communicate in either a synchronous or asynchronous way using a bidirectional communication channel. The proposed approach separates software engineering concerns, is easy to use, is reasonably efficient and enables the linking of arbitrary languages to graphical user interfaces