Is there a top-level object in any executing Ruby program? Is it the thing
called 'main' in irb?

Is so, why are top-level methods not made singleton-methods on this object,
instead of being pulled in as instance methods on the Object class itself
(and hence into all other classes i.e. more namespace pollution than is
usually intended). This would still allow top-level methods to call other
top-level methods. And if the top-level object were referred to by some
constant like Main, then those methods could be called from anywhere with
Main.method(...).