First public release of Arc came not long after Clojure.
Clojure is definitely better thought out as a language, and while Arc has some interesting ideas around web development, it also doesn't have a module system, so everything is just loaded into the same global namespace, which is pretty insane.
Keep in mind that Arc is the start of something with long-term goals; further, it's part of a lifecycle that didn't necessarily start with Arc but with the first Lisp. PG points to an early essay titled "The Hundred-Year Language" [1] as an indicator of where Arc is intended to go and some future outlooks that might inspire more evolution.
I don't know that any programming language can be everything it needs to be from the outset, but it certainly needs inherent featured supporting longevity, a framework that supports change and evolution, while still having a pleasing and useful function that can be taken advantage of immediately.
Ah, that makes sense. The next main difference in my mind is ergonomic, but relies on this regularity: functional syntax for composition, negation, quoted application. There are also other syntax additions and in my experience they're well-chosen and go a long way.
It would be more correct to say that they can be coerced to a function with a special purposes (e.g. using a set as a function is an alias for checking whether an item exists).
To say they are functions would be incorrect. By the same logic, a keyword is would be a function.
They're callable as functions, i.e. they implement clojure.lang.IFn. So unless you want to shave hairs on what it means to say they're not "functions", they _are_ functions. Sets, vecs, maps, keywords, and IIRC symbols are all IFn
Oh and (#{1 2} 3) is equivalent to (get #{1 2} 3) not (contains? #{1 2} 3)
I think that it depends upon what you interpret it when you say “it’s a function”; it’s data as well. Which, now that I reconsider it, was kind of the point that the parent was trying to make, that they’re also very much unified.
Clojure is definitely better thought out as a language, and while Arc has some interesting ideas around web development, it also doesn't have a module system, so everything is just loaded into the same global namespace, which is pretty insane.