I'll copypaste my comment that I've left at the HN discussion of that blogpost, https://news.ycombinator.com/item?id=23333853:

This is a PEBKAC, not a problem with REPL-driven development. He had all the test bodies written as input in the REPL, he had all the test results printed as output in the REPL. Why didn't he turn these into unit tests as he programmed?

That's a simple lack of foresight on the programmer's side that is then blamed on the tools that were used.

I knew his article would get misconstrued this way to clarify he almost certainly will be using a REPL in Clojure (even running tests happens through a REPL in Clojure) but I think what he's trying to convey there is that he's not designing in the REPL but rather with TTD

Which honestly is fine but most people reading the article won't be in a REPL based language like smalltalk or lisp so will just understand REPL bad TTD good

Not that I'm an expert but I guess he was doing it the wrong way. I just use (comment...) blocks to preserve what I entered into the repl. These blocks are also easily turned into test cases. It feels kinda similar to tdd.