I think `#inspect` can be used in this case.

```ruby
$ pry
[1] pry(main)> singletons = [nil, true, false]
=> [nil, true, false]
[2] pry(main)> singletons.map(&:to_s)
=> ["", "true", "false"]
[3] pry(main)> singletons.map(&:inspect)
=> ["nil", "true", "false"]
```