Don't forget examples
https://github.com/crystal-lang/crystal/search?q=pp&type=Code
https://github.com/crystal-lang/crystal-book/search?q=pp&type=Code

If examples used pp and now the behaviour changes, it not a big deal. In fact, in the two occurrences I found it only receives one argument, so the printed expression is really not needed in the output (and this is one of the things that couldn't easily be done before this PR).

I just mean that they should be updated, because their comments show output incorrectly.

Oh, I didn't see the output. Yeah, the should eventually be updated.

Please @asterite use a letter instead of !, we have the choice in the alphabet (like i).

When I see a bang for me the method needs to be used we caution, because it has a special behavior. This isn't the case here.

So...

a = [1, 2, 3]
a.map! { |x| x + 2 }

How is map! dangerous? Because it mutates a? Then the whole language is dangerous, everything keeps mutating.

The ! just means an alternative behaviour for a method. Rails choose to run validations on models. Ruby chose mutate or not mutate. Here we choose something different. Really, it's not a big deal, this is just for debugging purposes.

Plus we can change it later if we want to, because it can almost never be a serious breaking change because it's only used for debugging.

I dislike having 4 different methods, but 4 methods is what was agreed on in the issue.
Among the ways to name them, the one in this PR is my favorite, so I begrudgingly approve.