They have an interactive mode right now (crystal i), but it's not very comprehensive. You cannot use certain libraries with it etc.
Shouldn't be terribly hard to make it good though. Some time ago, I added a JIT REPL in a few afternoons with Claude, ending up with roughly the same performance as their compiler, and with it working reliably with all the libraries I tested. But since they don't want LLM contributions in Crystal, I just left it as an interesting experiment and started working on my own language instead.
Shouldn't be terribly hard to make it good though. Some time ago, I added a JIT REPL in a few afternoons with Claude, ending up with roughly the same performance as their compiler, and with it working reliably with all the libraries I tested. But since they don't want LLM contributions in Crystal, I just left it as an interesting experiment and started working on my own language instead.