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[NREPL-51] Pretty-printing reference returned by clojure.tools.nrepl.server/start-server causes multimethod exception Created: 12/Apr/14  Updated: 12/Apr/14

Status: Open
Project: tools.nrepl
Component/s: None
Affects Version/s: 0.2.3
Fix Version/s: 0.2.4

Type: Defect Priority: Minor
Reporter: Michael Nygard Assignee: Chas Emerick
Resolution: Unresolved Votes: 0
Labels: bug


I was accidentally printing the reference returned by start-server by calling it as the final function in my main method, which causes this error:

java.lang.IllegalArgumentException: Multiple methods in multimethod 'print-method' match dispatch value: class clojure.tools.nrepl.server.Server -> interface clojure.lang.IDeref and interface clojure.lang.IRecord, and neither is preferred
at clojure.lang.MultiFn.findAndCacheBestMethod(MultiFn.java:136)
at clojure.lang.MultiFn.getMethod(MultiFn.java:111)
at clojure.lang.MultiFn.getFn(MultiFn.java:119)
at clojure.lang.MultiFn.invoke(MultiFn.java:167)
at clojure.core$pr_on.invoke(core.clj:3266)
at clojure.core$pr.invoke(core.clj:3278)
at clojure.lang.AFn.applyToHelper(AFn.java:161)
at clojure.lang.RestFn.applyTo(RestFn.java:132)
at clojure.core$apply.invoke(core.clj:601)
at clojure.core$prn.doInvoke(core.clj:3311)
at clojure.lang.RestFn.invoke(RestFn.java:408)
at clojure.main$eval_opt.invoke(main.clj:299)
at clojure.main$initialize.invoke(main.clj:316)
at clojure.main$null_opt.invoke(main.clj:349)
at clojure.main$main.doInvoke(main.clj:427)
at clojure.lang.RestFn.invoke(RestFn.java:421)
at clojure.lang.Var.invoke(Var.java:419)
at clojure.lang.AFn.applyToHelper(AFn.java:163)
at clojure.lang.Var.applyTo(Var.java:532)
at clojure.main.main(main.java:37)

Comment by Michael Nygard [ 12/Apr/14 12:09 PM ]

I cloned this from NREPL-37, but cannot change any of the other fields. Thanks Jira.

Basically, this is the same dispatch problem as NREPL-37 but on clojure.pprint/simple-dispatch.

Version affected is 0.2.3.

Comment by Chas Emerick [ 12/Apr/14 12:21 PM ]

Thanks, should have thought of this when I fixed the related issue.

[NREPL-50] Configurable eval function Created: 10/Apr/14  Updated: 14/Apr/14

Status: Open
Project: tools.nrepl
Component/s: None
Affects Version/s: None
Fix Version/s: 0.2.4

Type: Enhancement Priority: Minor
Reporter: Brandon Bloom Assignee: Chas Emerick
Resolution: Unresolved Votes: 1
Labels: patch, patch,

Attachments: Text File 0001-NREPL-50-Overridable-eval-function.patch    
Patch: Code


#'clojure.main/repl has an :eval keyword option that is currently not provided by the interruptable-eval middleware.

I'd like to be able to supply that argument on a per session basis.

Comment by Brandon Bloom [ 10/Apr/14 7:36 PM ]

Attaching patch to support :eval option on (= op :eval) messages.

Comment by Chas Emerick [ 11/Apr/14 7:20 AM ]

This patch adds that option on a per-evaluation basis, which I don't think you really want. Having this set on a per-session basis (as you originally described) makes more sense to me, esp. insofar as doing it that way makes it trivially controllable from "userland" (i.e. the human typing in expressions to be evaluated somewhere). Changing the shape of messages going back and forth requires tool support.

Comment by Brandon Bloom [ 11/Apr/14 9:44 AM ]

Ah, sorry, I should have explained why I ultimately did this at the per-message level. I've got a custom evaluation, but I want to be able to freely mix standard and custom evaluations during the same session. In my case, I have .clj files that use clojure.core/eval and .eclj files that use eclj.core/eval via vim-fireplace. As far as I can tell, Fireplace only opens one session per lein project, so session variables would have been a lot more work.

Is there some way that I can easily override session variables on a per message basis? If so, then I can switch to that to get both the user-level customization and tooling-level support. Otherwise, I'm open to suggestions.

Comment by Chas Emerick [ 12/Apr/14 12:40 PM ]

Sessions are essentially just the result of get-thread-bindings, plus some nREPL bookkeeping. So, as long as evaluate binds e.g. *eval*, users can just set! the var to change it. Though, unless you watch for that in your custom evaluation fn, you'll never be able to change it back. :-P This seems like a good enough reason to keep the option per-message, and require tools/users to ask for what they want each time.

(Tangentially, I just remembered that Piggieback does roughly the same thing you're looking for. I thought about pushing something like what you're suggesting down into nREPL, but I'm very cautious about changing it to suit my needs [myopia and so on]. Glad we have a second real use case, which makes me feel better about the whole thing.)

Comment by Brandon Bloom [ 13/Apr/14 12:09 PM ]

Yeah, set! seems like a surefire way to steamroll over later evaluations unless everybody does a defensive set! all the time, and even then, set! may not even be defined for the evaluator that the caller is expecting!

Maybe this means that there needs to be some sort of general-purpose way to override session variables per message? Then, we'd only need to define eval and all messages could be processed inside their own with-bindings call.

Comment by Chas Emerick [ 14/Apr/14 2:13 PM ]

Maybe, but that's a lot to bite off without having more than "wouldn't it be cool if…" as motivation.

Any thoughts as to whether the eval symbol's namespace should be implicitly {{require}}d?

Will be applying the proposed patch (maybe with a tweak or two) this week.

Comment by Brandon Bloom [ 14/Apr/14 2:23 PM ]

Clojure's standard load-file looks for .class or .clj files. EClj has to patch the loader to look for .eclj files too, and eclj.core may be re-loaded after the new evaluator is bootstrapped.

I have to pre-load the namespace manually either way. Therefore, I don't care if it implicitly requires the namespace, as long as it doesn't :reload the namespace.

[NREPL-48] *1/*2/*3/*e nil in cloned session Created: 02/Jan/14  Updated: 02/Jan/14

Status: Open
Project: tools.nrepl
Component/s: None
Affects Version/s: None
Fix Version/s: None

Type: Defect Priority: Minor
Reporter: Tim Pope Assignee: Chas Emerick
Resolution: Unresolved Votes: 0
Labels: None


Summary says it all. This isn't blocking me; just something I stumbled onto.

[NREPL-43] Document the availability/usage of *e, *1, *2, ... in nREPL Created: 04/Jul/13  Updated: 24/Aug/13

Status: Open
Project: tools.nrepl
Component/s: None
Affects Version/s: None
Fix Version/s: None

Type: Enhancement Priority: Minor
Reporter: Jakub Holy Assignee: Chas Emerick
Resolution: Unresolved Votes: 0
Labels: documentation


I have only by chance discovered that nREPL binds the lat error/outputs to the vars *e, *1 etc. This should be documented clearly somewhere, possibly in https://github.com/clojure/tools.nrepl/blob/master/README.md

When I have forgotten the names of the vars while remembering that something like them exists, I tried to google them out but failed. So better documentation would help.

Thank you!

Comment by Chas Emerick [ 04/Jul/13 7:07 AM ]

The role of those vars is actually the same across all Clojure REPLs. In this department, nREPL is simply following Clojure's lead.

That said, yes, there is room to specify fully what nREPL's behaviour is, beyond the implied equivalence (at a minimum) to Clojure's included console REPL.

Comment by Jakub Holy [ 22/Jul/13 7:37 AM ]

Thank you for the clarification!

> The role of those vars is actually the same across all Clojure REPLs.

Do you know if this behavior of all Clojure REPLs is documented anywhere? And yes, it would be nice if the nREPL documentation linked to this doc and/or it printed a short summary and/or link when starting (in addition to the currently provided info about (source) etc.)


Comment by Chas Emerick [ 22/Jul/13 7:52 AM ]

REPL-bound vars are documented in a variety of places, though nowhere "official" AFAIK. We talked about it in Chapter 10 of Clojure Programming FWIW (I'm certain other books and online resources cover these vars as well, but the CP citation is the only one I have close at hand.)

FYI, the "currently-provided info" you mention is emitted by Leiningen/Reply, not nREPL.

Comment by Jakub Holy [ 24/Aug/13 4:50 AM ]

Thanks a lot, Chas, that was helpful. I have submitted a patch to Leiningen to include the info it its REPL' welcome message: https://github.com/technomancy/leiningen/pull/1310

Comment by Jakub Holy [ 24/Aug/13 5:38 AM ]

I have published a blog post about this, Clojure REPL stores the latest results in *1, *2, *3, exception in *e, to make it more googlable (is that even a word? ).

The top hit for "Clojure REPL" seems to be http://clojure.org/repl_and_main, so it perhaps should be documented there or it should link to a more detailed documentation. Not sure how to make that happen I have also checked http://clojure-doc.org/ but there doesn't seem to be a suitable place to add this info either. Perhaps it should be mentioned in the docstring of clojure.main/repl and the Clojure page should link to it?

Comment by Jakub Holy [ 24/Aug/13 5:52 AM ]

I have created an issue under Clojure itself, #CLJ-1247, so this can likely be closed.

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