That's what I thought too when I first saw it. But then I actually took a moment to read it and eventually changed my mind.

What would your ideal version look like? I recommend reading the C++ or Rust equivalent code in the article. I like the example because it is copied 1:1 with example code from a textbook with only some keywords changed and a Copy constraint. Any other language without a GC and with unboxed types today represents it far more verbosely to the point where the meaning becomes obscured and a typo becomes more likely to survive code review.

surprised to see that, I've long held tree balancing up as practically the poster child for ML syntax being the best way to express certain algorithms. it directly says what shape of nodes goes to what other shape.