oko1,
Recently, I was thinking about that example in the docs where they demonstrate a method for inserting commas into a numerical string.

You mean the one from perlfaq5?

but that thing is just clumsy and awful and obfuscated for any Perl beginner. So, just for my own entertainment, I decided to see how I'd do it "for real" - i.e., in the best way possible rather than by this contrived method.

I agree that many of the solutions in the FAQ are written more as a cook book rather than as a tutorial. On the other hand, do you honestly feel that your solutions are any better if your target audience is a perl beginner?

If that is your target audience, I would have gone with something a bit more verbose.

• Return undef if input is not numeric - perhaps using Scalar::Util's looks_like_number()
• Return input in tact if it shouldn't be commified (Inf, NaN, already commified, etc) - perhaps using a different sub
• Perform commification in step-by-step atomic units of work

Since it seems your intended goal was to educate beginners, each step should be preceded by the appropriate amount of comments. It may not be obvious what a regex is doing so you could recommend YAPE::Regex::Explain. They may not have considered edge cases, so rather than incorporate them into a single step that is doing something else - break it out on its own statement.

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