[zsyllepsis]

I think the author’s choice of function to demonstrate purity made this harder to grok as a reader. Asking the reader to “…exclude the I/O interactions…” when considering functional purity makes the analogy much harder to follow.

My interpretation of the thesis of that paragraph is that localized mutation does not violate referential transparency, but getting there required some gracious reading. By the end of the section, we’re given an _example_ of an effectfully pure function, but no standalone definition.

Based on that, I agree that this is a weak point in the overall piece.