Creating a top level definition if none so far exists, on the fly.

[Richard Shann]

I have just started using GNU/Denemo under the guile 2.x and the
following construct no longer works:

(if (not (defined? 'ToggleFiguredBassMode::Active))
    (define ToggleFiguredBassMode::Active #f))

The intention is to have a variable defined at the top level which
starts out being #f. The need for the construct arose because it
appears in a self-contained script which cannot expect an
initialization step to have been performed.
Is there a straight-forward way to modify this?

Richard