Felix,

> Wouldn't it perhaps be better to make "default-random-source"
> a procedure?

In fact, I am not very happy with default-random-source at all.
The problem is that one has to maintain two related objects
(the generator procedure and the random source object) in
the application without having seeing an explicit relationship.

You proposal solves part of the problem, but unfortunately
only part of it. I will continue to think about it and come back
to it later.

Sebastian.