Another question about this issue: in the case of `:a*` for example, why doesn't it just pick empty string as the replacement text and immediately exit? Why would it be an infinite loop if `-g` isn't specified?

And then if `-g` were specified, you could use this to create infinite generators, which could be a useful construct in some cases -- like `yes` but more powerful.

EDIT: Another interesting use case, if I am understanding correctly: if this worked, then you could use `:(<regex>)` to have it output an example of a string that matches any given regex. `-g :(<regex>)` produces a generator of every string in the language matched by that regex. `-g :(<regex>) | head -n 100` would give you 100 examples.