If I may be so bold to interject -- I'm a colleague of Didier's, and I originally brought this to his attention when I hit this issue at work. I just want to add that part of the confusion arises from some miscommunication/incomplete information on the official docs for Namespaces <https://clojure.org/reference/namespaces>;
At the Repl it’s best to use in-ns > <https://clojure.github.io/clojure/clojure.core-api.html#clojure.core/in-ns>, > in which case the new namespace will contain mappings only for the > classnames in java.lang. In order to access the names from the > clojure.core namespace you must execute (clojure.core/refer > 'clojure.core). The user namespace at the Repl has already done this. The current namespace, **ns** can and should be set only with a call to > in-ns > <https://clojure.github.io/clojure/clojure.core-api.html#clojure.core/in-ns> > or > the ns macro > <https://clojure.github.io/clojure/clojure.core-api.html#clojure.core/ns>, > both of which create the namespace if it doesn’t exist. I believe this is a major source of the confusion (at least it was for me). The official documentation *does* mention that in-ns is recommended in the REPL; and in a subsequent paragraph, the official documentation *does* state that in-ns (or ns but it macroexpands to in-ns as well so is just as bad in context) is the preferred way of creating a namespace. But nowhere on the official documentation page does it qualify that *ns*, as a dynamic Var, will require curation if bootstrapping an application from a static context! Instead, users are thrown with the ugly IllegalStateException("Can't change/establish root binding of: *ns* with set"), which is fairly inscrutable in context. (Nowhere else that I'm aware of in the runtime can a user not have ever created a dynamic var themselves, have manipulated it without realizing they're using the set! API, and end up trying to set! it at runtime before calling binding.) It's not a lie or intentionally misleading, but allows an application developer to walk away with an incomplete and inconsistent understanding of the operation of those functions. Somehow the logical decision was taken at every step, but yet there's room for users to trip up here. People who tinker with macros and evals are probably accustomed to battling issues with dynamic vars, or at the very least are remembering that dynamic vars have different semantics, and so can easily search online to discover that they ran afoul of the Var stack frame issue and need to add a binding. But in-ns is a real head-scratcher! If implemented in Clojure, it would look like (set! clojure.core/*ns* (create-ns 'some-namespace)), but because it's defined in RT.java, there's no source available; what's more, the documentation attached to the Var for in-ns doesn't allude to the mechanics it employs. Hands down I can guarantee all Clojure developers who aren't involved in the language maintenance will respond to the exception above by thinking, "Let me check the source using the source macro and see what just happened." They'll call clojure.repl/source and get -- nothing. Then they'll check the docs which say -- "Sets *ns* to the namespace named by the symbol, creating it if needed." While *technically* correct, this is hands down more likely to be read in the colloquial English meaning of "casually changes", rather than the Clojure-technical meaning of "Does something akin to calling `set!`". And they'll either give up after an hour of fruitless searching, or if they have *a lot of free time*, will spend several hours poring over compiler source code <http://justabloginthepark.com/2017/06/18/clojure-and-the-esoteric-mysteries-of-namespaces/> until they realize that nobody documented this case; and that the mechanics at runtime, while internally consistent, are completely counter-intuitive given the information available on the public documentation. I'm glad that you're considering "plugging" the other Clojure entry points to eliminate this stumbling block altogether. In the meantime, perhaps some clarification of the documentation (either those attached to the Var itself, or on the site, or both) are in order? Thanks, - Jeff On Thursday, June 22, 2017 at 3:47:17 PM UTC-4, Didier wrote: > > I opened a Jira enhancement: https://dev.clojure.org/jira/browse/CLJ-2185 > > Hope I did a good job at it. > > On Wednesday, 21 June 2017 18:58:26 UTC-7, Alex Miller wrote: >> >> Was just musing some more - the Clojure Java API was added pretty late >> (~1.6 or 1.7). I wonder if >> >> 1) changing the Java Clojure API to ensure a certain binding context and >> 2) changing the main() method to invoke the Clojure function through the >> Java Clojure API >> >> would be a good end game. Would need a lot more analysis. >> >> On Wednesday, June 21, 2017 at 8:52:48 PM UTC-5, Alex Miller wrote: >>> >>> >>> >>> On Wednesday, June 21, 2017 at 6:09:43 PM UTC-5, Didier wrote: >>>> >>>> Great breakdown. >>>> >>>> 1. "compile and bootstrap yourself through gen-class" means: you >>>>> generate a class and then invoke the main() method of that class >>>>> >>>> >>>> I'd go further then just calling main. So I mean you generate a class, >>>> and every function call from Java using the generated class should be >>>> executed as if it were executed through clojure.main, so with the bindings >>>> set and inside the user namespace. >>>> >>> >>> I do not think you should treat clojure.main as the gold standard. >>> clojure.main is a helper program and it makes some choices that may or may >>> not be what every program wants. There is nothing special about the "user" >>> namespace for example. Other repls choose other things (pretty sure the >>> boot repl uses boot.user example). Likewise, there's nothing special about >>> the set of things clojure.main chooses to bind on startup - lein, boot, and >>> other tools make different choices. If anything, I'd say #2 is what you >>> should consider the most canonical case. >>> >>> >>>> >>>> >>>>> 2. "loaded at runtime" means: you (presumably) start the REPL, load a >>>>> namespace (either from a source file or a class file), then invoke the >>>>> -main function >>>>> >>>> >>>> Correct. It's the case of a non AOT compiled namespace being loaded >>>> from one of the many (load) functions of Clojure. Such as: >>>> >>>> (load "dda/main") >>>> (dda.main/-main) >>>> >>>> >>>>> 3. "bootstrapped through clojure.main" means: you invoke clojure.main >>>>> (a compiled program provided with Clojure) with the -m arg specifying a >>>>> namespace. This will start the Clojure runtime, load the namespace, then >>>>> invoke the -main function >>>>> >>>> >>>> Correct. >>>> >>>> >>>>> 4. "bootstrapped through lein" means: I assume this is "lein run" with >>>>> a :main set or "lein run -m" but I think lein supports specifying a >>>>> namespace or a function in a namespace or a class with a main() method. >>>>> Depending which of those you're doing, this is like similar to either #1 >>>>> or >>>>> #2 and here lein is effectively doing similar work as #3. >>>>> >>>> >>>> Correct, yes internally lein delegates to clojure.main I believe. >>>> >>> >>> No, I don't think lein uses clojure.main at all. >>> >>> >>>> >>>> >>>>> 5. There is a Clojure Java API ( >>>>> http://clojure.github.io/clojure/javadoc/), but I'm not sure if you >>>>> are actually referring to this or something else. Doing so would >>>>> basically >>>>> mean going through that API to do the same thing as #2. >>>>> >>>> >>>> I am talking about that API. I believe it uses RT under the hood, and >>>> ends up doing the same thing that #1 does. So in my test, if you did: >>>> >>> >>> This is actually the same as #2, not #1. It's not making an interop >>> call, it's invoking a var function, just like any other Clojure call. >>> >>>> >>>> IFn require = Clojure.var("dda.main", "-main"); >>>> require.invoke(); >>>> >>>> This will run inside "clojure.core", and will not have any of the >>>> default bindings set available. >>>> >>>> I think if I were to restate your suggestion, I would say that a >>>>> genclass-compiled main entry point should initialize the Clojure runtime >>>>> and invoke the code in a binding as if it were being invoked from other >>>>> Clojure code. I can see some logic in that (although that then also >>>>> affects >>>>> #3 and #4 as they go through this code too). >>>>> >>>> >>>> Ya, arguably, I wonder why the clojure runtime doesn't initialize the >>>> bindings and sets the namespace to 'user before delegating execution back >>>> to user code. >>>> >>> >>> Again, there is nothing special about user and I wouldn't get hung up on >>> that. It does seem like it would be reasonable to set up a binding context >>> for *ns* though so it's set!-able - that's the thing that's missing. >>> >>> >>>> If it did, then every invocation of Clojure from Java would always be >>>> bootstrapped in a similar way, and run under an equal context. >>>> Clojure.main >>>> wouldn't need to do it anymore. >>>> >>>> But there might be a good reason for not doing that inside the clojure >>>> runtime. In which case, it still leaves open the question of should >>>> clojure >>>> invocations through a generated class, and invocations from the Clojure >>>> API >>>> mimic the bootstrapping of clojure.main? >>>> >>> >>> I would say, no. :) But it might be reasonable to mimic a Clojure >>> function invocation that has a binding for *ns*. If you want to file a >>> ticket, I'm happy to think about it more. >>> >>> >>>> >>>> P.S.: I also know that in practice, this has not caused that many >>>> issues, due to the fact that Clojure is now many years old, and I've never >>>> heard of other people complain about the discrepancies between generated >>>> classes and the clojure API versus clojure.main. So I don't think its a >>>> pressing issue, but I still feel it could be worth a thought. >>>> >>>>> -- You received this message because you are subscribed to the Google Groups "Clojure" group. 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