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Comment by kaffeinecoma | Hacker News Reader

> a REPL. Just give it a whirl and see what you get.

In a large system you might have to jump through a lot of hoops to get an accurate result from the REPL. What if the thing you're trying to puzzle out is 20 call levels deep? As a new Ruby dev I struggle with this.

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In python if I was trying to figure out something complex 20 levels deep, I would stick in an "import pdb; pdb.set_trace()" to get a REPL at that spot. There's probably an equivalent for Ruby?

(Off-topic, the werkzeug debugger even lets you debug browser apps by jumping into a REPL anywhere in the stack trace, in the browser, after an exception is thrown. I think it also has a command that bakes you a pie.)

If it is a pure function it makes the call depth irrelevant. While not always the case, it seems to be pretty common in Ruby development to keep things as pure as possible.

No, it's not irrelevant. If you're trying to figure out what gets passed up the call stack, you need to trace it through. Being able to plug in your own values into a single method call via the REPL isn't helpful if you're trying to analyze what really happens when it runs. Either you need to run it under a debugger, or manually trace it through. In a static language you just have to read the type signatures.

As mentioned by JackC, if you need to understand the context in which a method is called, use a REPL. But to understand what a pure method does should be context free, by definition.

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