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Scientific debugging might also be called "repl-driven debugging". It's basically executing expressions from your program at the repl to pinpoint the source of a problem. You form a hypothesis (a guess about where the bug is), do an experiment (run an expression), and analyze the results.
Keeping code in sync
When you're doing Repl-Driven Development, your repl and the code in your files can get out of sync. The first step is to diagnose whether it is the code or your repl that is broken. Once diagnosed, the fixes are usually straightforward. Either way, it can be frustrating, but knowing is half the battle.