It only makes more sense when you do look at the background, so thanks for the link. They're lisp folks. They use kebab-case. I completely get it. It may be the product of decades of research, but it is also the product of default choices and comfort for the people who wrote it. ALL programs have an element of this: I write Rust and you can tell without looking when some tool is written in it -- TOML config? Apache-2.0/MIT dual-licensed? Few such decisions have no downsides, and yet exceptions are rare.

It takes a lot to make a choice for reasons other than your own familiarity. From the linked thread, they clearly agonized over this. Apparently they talked themselves down from the usual Lisp ultra-permissiveness on idents, so good on them -- but it was still explicitly a compromise between their comfort and the aims of the project.

There is an obvious and very good reason why the number of languages that do this can be counted on one hand. The authors know that. It is a problem they decided to accept because it was the default for them, and they "just couldn't give up on how pleasing hyphens in identifiers are to the eye and the shift-finger", and then mitigated it via other whitespace changes. They were content when "Anecdotally, no one in our courses ha[d] complained". I disagree with it. I find it really hard to read. I guess I am used to other languages, but so is everyone who has dabbled in python, likely writing primarily numeric code for their stats/bio/physics courses.

Consider me a student reporting it as a problem. Consider the 2013 thread a student reporting it as a problem as well. How about that?

I'll finish with a quote from Krishnamurthi himself: "Saying 'add spaces around binops' is easy to learn, recognize, and implement."

Does this not speak for itself?

    fun subtract(a, b):
      a-b
    end
    
    >>> The identifier a-b is unbound:        definitions://:3:2-3:5
    
    4 | a-b
    
    It is used but not previously defined.

Edit: I dug up an old thread from the guy @estebank who makes all the amazing Rust error messages, responding to a paper of Krishnamurthi's that argues, true to form, that you shouldn't ever actually "Say 'add spaces around binops'" (https://twitter.com/ekuber/status/1140791186858266624). The paper itself is an interesting read, particularly the interviews where beginners don't have the vocabulary to decipher error messages. But I think Esteban is right.