[gtk-server] Using GTk macros or properties

I'm trying to determine whether a given widget is visible. I found
this in the GTK docs:
1. GTK_WIDGET_VISIBLE() (which is a macro)
2. The "visible" property
(source: http://developer.gnome.org/doc/API/2.0/gtk/GtkWidget.html)

But I can't get these to work. I believe it's because they are not
functions; I've only used functions (e.g. gtk_window_set_title) until
now. I tried various ways of writing my GTK-server call but all I got
as a result was -1, regardless of the widget's visibility -- the same
as when I write rubbish.

Can somebody give me an example for using these? I'm new to both
GTK-server and GTK, so don't hesitate telling me obvious stuff. I'm
using CLisp with Linux.

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