As projects get bigger, things might get sadder. I worked at a certain large SF company that uses a lot of ruby, so most development was repl-based too. But this wasn't a boon but a curse, as the total lack of data format guarantees on the very large, critical monorepo meant a lot of uncertainty. What does this method really do? I guess we have to run it! It worked for this specific input... but will it work for any and all inputs that get to this data path? Let's hope so, because we aren't sure! The company spent massive amounts of money on servers for parallel testing, just so that the suite could run in less than a few weeks. And when you need a large test suite to have a chance, most of the advantages of the REPL vs a compiler have been lost.

Eventually they did the same thing you can do in common lisp: Add so much metaprogramming that doublechecks invariants, it might as well be a compiled language.