Perhaps check if Unicode.category/1 returns :Lu.

EDIT: Just noticed that there is also Unicode.uppercase?/1 which does this exact check.

I was about to suggest ex_unicode as well, but given the nature of this being an exercise I doubt they expect people to use an external dependency.

Just a hint, I don’t think you need to check every codepoint individually, but instead try to work with the whole string input and just the String module.

Unicode is from ex_unicode package.

Alternatively if you want to stay with standard library, check out Regex character classes which include alpha and upper.

When I first solved Bob, I did so entirely with the Regex module. One of the comments my mentor made, was that, although Bob can be solved many ways, the intent of this exercise (on the Elixir track) is to get you familiar with the String module. I was encouraged to return to the String module, and solve the exercise without using any regexes at all. The solution I came up with turned out to be much more elegant than the regex solution, and indeed required only functions from String.

Here is a hint to get you started: Under what conditions would the uppercase version of a string be the same as the original? Are there other relationships like this you can leverage?