You're spot on about the quirky syntax, but I don't think it's as serious a trade-off or addition in complexity (or even a change), given that:
- (IIRC) many style-guides/formatters already enforce spaces between binary operators and their operands (but especially identifiers) and in my super-subjectively-opinionated opinion you should already be doing that even without a formatter
- I don't feel particularly strongly one way or another about any other special characters like "+", so really in this case I'm only considering the dash
- Requiring the dash between alpha/alphanumerics makes it play nice with unary operators
- The language would be terrible for code-golfing, but that's a relatively niche application I'd definitely consider worth spurning
This is a gross error. In your sense, Lisp does not even have operators, only identifiers. The reason there is no confusion between "(- a b)" and "(-ab)" is the spacing that separates the three identifiers in the first case.[1]
Your comment is especially weird because you go on to discuss Lisp's approach as being "an alternative option to what Lisp does".
[1] However, Lisp does have a potential problem with identifiers that begin with a hyphen, due to the need to support literal numeric values like -3. Thus the Common Lisp decrement function is named "1-" despite not returning the value (1 - operand).
I assume you're talking about GP's third paragraph here. Assuming that's true, I think you've misinterpreted it: GP was talking about using infix operator notation, which is most certainly not what Lisp does.
Lisp will treat (a - b) as 5 tokens, just the same way it will treat (- a b) as 5 tokens. Infix operators are completely unrelated to this problem. What lisp is doing is determining tokens by reference to spacing (the parentheses don't need to be spaced; I believe they are reader macros but in any event they are special-cased) and then acting on the tokens. What C is doing is not that; the concept is that you eliminate all spacing before you decide what the tokens are.
So in C, there is no such thing as "a - b", only "a-b", and that's why "a-b" cannot be used as an identifier.
If you want to write your lisp in infix notation, you can, but it will remain true that (a - b) is a list with 3 elements and (a-b) is a list with 1 element, which is what matters here.
> First obvious option is to get rid of the infix "-" operator, which is what Lisp does. In lisp-like languages you don't write "a - b" instead you write "- a b", this way there is nothing to confuse "a-b" with.
> Another option is to require a space between operators. E.g. you are not allowed to write "a+b" to mean "add a to b". You have to write "a + b". This is used in Agda programming language.
is kinda not good, Lisp allows "-" in names the same reason as Agda: it tokenize by spaces (correct me if I'm wrong). This may seem as a gross error for one, and an only implied who cares error which is even true if taken word-by-word, for an other.
I would say the trade off is variable names like “a+b” themselves. I fail to see any reason why would I want something like that, like even in Math where the grammar is very hand-wavy to accommodate human parsing you would be insane to write that (though to be fair, math does have their own share of problem with identifiers, enumerating all the letters in different alphabets is not a sustainable solution)
First obvious option is to get rid of the infix "-" operator, which is what Lisp does. In lisp-like languages you don't write "a - b" instead you write "- a b", this way there is nothing to confuse "a-b" with.
Another option is to require a space between operators. E.g. you are not allowed to write "a+b" to mean "add a to b". You have to write "a + b". This is used in Agda programming language. This is very useful because then you can have identifiers like "a+b", or even identifiers like "a+[b+c-d]" etc... As long as any char doesn't have a special meaning (e.g. in Agda "(", ";", "," etc have special meanings) you can use it in an identifier. The trade-off is that, well now you're not allowed to condense arithmetic operations. This may or may not be a problem, depending on the programming language designer. When you said:
> I strongly suggest you either reconsider or never write any code you think may be read by another human being (and possibly yourself).
I'm guessing your opinion is that you're ok with this trade-off. Fact of the matter is that this a very fringe syntax for any programming language to have. As an Agda programmer, I like it, and it is useful, but I'm not convinced something like this would find mass appeal.
The last option I'm aware is to have semantic differentiation. When you find a statement like "c = a-b" you need to ask two things. One, are there identifiers "a", "b" and "a-b". If "a-b" exist and "a" or "b" doesn't exist, you're all set. If all three exist, second question is, are "a" and "b" subtractible? If the answer is yes then programming language designer can choose to prioritize "a - b" over identifier "a-b". Alternatively, you can always choose to prioritize identifier "a-b" as long as it exists. I'm personally not aware of any language that implements something like this, however I have implemented toy languages that go through this, it's pretty easy. It's a matter of making the decision to introduce this type of complexity into your language.
All in all, although I love kebab case, in order to have it in your language you need to make pretty significant trade-offs. Given this, I'm not surprised any mainstream non-lisp-like language doesn't have it.