It is certainly less axiomatic--you don't need this to have a working Lisp. However, it's useful (I needed it to do my little module system), it's likely to be very simple to implement as a primitive (given access to Scheme, we can just use 'namespace-set-variable-value!), and its name clearly maps to its function and its setf behavior. (I'd be inclined to use the name "global-value" or "symbol-value", actually.)
Finally, it's easier to see "symbol-value" written in the language description and use it than to figure out how to use the 'eval method properly. Just look at how complex your definition is; even I, who do see why it's necessary to go ',desired-value instead of ,desired-value in my version [if objs in code worked properly, you could use the former version for a while without noticing it was wrong], I don't see why it's necessary to go (',(fn () desired-value)), and I certainly wouldn't think of it myself. (I still don't believe it's actually necessary, but I won't press the point.) Like the case of (++ (car (pop xs))), this is one of the things a core language is good for: the implementor has considered and avoided all the subtle pitfalls for you. (Actually, implementing it as a primitive with the "namespace-..." functions, there aren't any pitfalls to avoid.)
By the way, I don't know if the core of the language is supposed to be all that axiomatic. It should be clean, certainly, but by its nature it should provide more than minimal axioms. In an essay[1], Paul Graham talks about "the core language—those operators that are neither primitives like car and cdr, nor special-purpose library functions. I mean operators like CL's mapcar, let, remove-if-not, and so on."
At any rate, here's what I think: (a) There will be people who need the equivalents of 'symbol-value and (setf symbol-value)--people who write module libraries or debugging facilities or for whatever reason[2] want to determine names at runtime. (b) This might be enough by itself to warrant placement in the core language, but (c) it is extremely easy, not to mention efficient, to implement these as primitives, while it is subtle, error-prone, and inefficient to implement it with 'eval. Therefore, it should be built into the language. (Technically, if it's a primitive, then it's not part of the core language by the implicit definition from the essay, but whatever you call it, it should be built in.)
I feel better about rambling/ranting when I also produce something tangible, like working code. So, here you go:
That's why it's in Lathe, too. ^_^ Since it's there to implement the module system, it's one of only a couple dozen Lathe utilities that isn't in a module, but I find it useful enough that I like it that way.
I don't see why it's necessary to go (',(fn () desired-value))
If you embed a literal vector in an expression (for instance, a tagged value), Racket will evaluate that expression as a copy of the vector. So (let foo (annotate 'a 'b) (= global!x foo) (is global!x foo)) would return nil, which I find frustrating. ^^ (There might be significant mutations-aren't-reflected-in-both-copies gotchas too, but I'm not sure right now.)
If you embed a procedure instead, I don't know if it copies that too, but it doesn't matter 'cause a copy of the procedure should still close over the same bindings. In practice, (let foo (annotate 'a 'b) (= global!x foo) (is global!x foo)) works, so I'm satisfied.
By the way, I don't know if the core of the language is supposed to be all that axiomatic. It should be clean, certainly, but by its nature it should provide more than minimal axioms.
This is a point I just acknowledged but challenged at http://arclanguage.org/item?id=13266. I'm not sure entirely whether and how I (dis)believe it, so a response is welcome. ^_^
it is extremely easy, not to mention efficient, to implement these as primitives, while it is subtle, error-prone, and inefficient to implement it with 'eval.
Sure. Implementing 'symbol-value in terms of 'eval is a pretty big abstraction inversion, and it causes lots of unnecessary consing and compilation at runtime. I'm kinda conviced. ^_^
working code
Incidentally, official Arc allows you to say (assign a.b t) and observe (bound 'a.b). Your 'symbol-value makes it possible to get the value of 'a.b again, whereas there's no non-exploit way to do that with 'eval. ^_^ (You can use the (cdr `(0 . ,_a.b)) bug, lol.)
Speaking of 'bound... why is 'bound a primitive when 'symbol-value isn't? XD Actually, I've wondered why 'bound was a primitive for a while, but that kinda-convinces me further. ^_^
