Author describes a nice feature, but that’s not what makes repl-driven development tick for me. Repl really shines when editor integrates with it - send a form to evaluate, instantly get result back into the editor, eval a form and replace it with the value received, define and redefine the environment on the fly, get instant feedback if your code works without having to drop into shell and run some test command, micro-tests and usage examples that you can actually run inside editor to see how they work.

You can get similar integration with ruby and python, but there’s way more friction because that kind of development is not the blessed way and so nobody bothers to make it work.