You can use a REPL powered debugger. You can interact with the debugger to a higher degree than with most mainstream languages. It’s not quite as powerful as CL

You can use a REPL powered debugger. You can interact with the debugger to a higher degree than with most mainstream languages. It’s not quite as powerful as CL though, from what I’ve read. Or you pull out expressions and test them in isolation with given (assumed) inputs.