clojure.stacktrace/root-cause VS clojure.repl/root-cause, are they redundant?

[Pierre Masci]

Hi, I'm learning about tools to help me debug from the REPL, and I found these two with the same name:

    clojure.stacktrace/root-cause

    clojure.repl/root-cause

For a very simple case (wrong arity), they give pretty similar output:

    user=> (char 0 0 0)

    CompilerException clojure.lang.ArityException: Wrong number of args (3) passed to: core/char--inliner, compiling:(/tmp/form-init6819528724684564936.clj:1:1) 

    user=> (clojure.stacktrace/root-cause *e)

    #<ArityException clojure.lang.ArityException: Wrong number of args (3) passed to: core/char--inliner>

    user=> (clojure.repl/root-cause *e)

    #<CompilerException clojure.lang.ArityException: Wrong number of args (3) passed to: core/char--inliner, compiling:(/tmp/form-init6819528724684564936.clj:1:1)>

I looked at the source code and they look fairly similar, but I didn't understand the exact details.

If they do the same job, then which one does it best?

If they perform different roles, then could you describe the difference to a user who doesn't need to understand the internals? ( I'm happy to understand them if you are willing to explain, though :) )

[Pierre Masci]

I have now noticed that these two are also very similar:

    clojure.stacktrace/print-stack-trace

    clojure.repl/pst    ; (for Print Stack Trace)

Here is their output for the same error:

user=> (char 0 0 0)

CompilerException clojure.lang.ArityException: Wrong number of args (3) passed to: core/char--inliner, compiling:(/tmp/form-init9068522213039312274.clj:1:1) 

user=> (clojure.stacktrace/print-stack-trace *e)

clojure.lang.Compiler$CompilerException: clojure.lang.ArityException: Wrong number of args (3) passed to: core/char--inliner, compiling:(/tmp/form-init9068522213039312274.clj:1:1)

 at clojure.lang.Compiler.analyzeSeq (Compiler.java:6651)

    clojure.lang.Compiler.analyze (Compiler.java:6445)

    clojure.lang.Compiler.analyze (Compiler.java:6406)

    clojure.lang.Compiler$BodyExpr$Parser.parse (Compiler.java:5782)

    clojure.lang.Compiler$FnMethod.parse (Compiler.java:5217)

    clojure.lang.Compiler$FnExpr.parse (Compiler.java:3846)

    clojure.lang.Compiler.analyzeSeq (Compiler.java:6642)

    clojure.lang.Compiler.analyze (Compiler.java:6445)

    clojure.lang.Compiler.eval (Compiler.java:6700)

    clojure.lang.Compiler.eval (Compiler.java:6666)

    clojure.core$eval.invoke (core.clj:2927)

    clojure.main$repl$read_eval_print__6625$fn__6628.invoke (main.clj:239)

    clojure.main$repl$read_eval_print__6625.invoke (main.clj:239)

    clojure.main$repl$fn__6634.invoke (main.clj:257)

    clojure.main$repl.doInvoke (main.clj:257)

    clojure.lang.RestFn.invoke (RestFn.java:1096)

    clojure.tools.nrepl.middleware.interruptible_eval$evaluate$fn__591.invoke (interruptible_eval.clj:56)

    clojure.lang.AFn.applyToHelper (AFn.java:152)

    clojure.lang.AFn.applyTo (AFn.java:144)

    clojure.core$apply.invoke (core.clj:624)

    clojure.core$with_bindings_STAR_.doInvoke (core.clj:1862)

    clojure.lang.RestFn.invoke (RestFn.java:425)

    clojure.tools.nrepl.middleware.interruptible_eval$evaluate.invoke (interruptible_eval.clj:41)

    clojure.tools.nrepl.middleware.interruptible_eval$interruptible_eval$fn__632$fn__635.invoke (interruptible_eval.clj:171)

    clojure.core$comp$fn__4192.invoke (core.clj:2402)

    clojure.tools.nrepl.middleware.interruptible_eval$run_next$fn__625.invoke (interruptible_eval.clj:138)

    clojure.lang.AFn.run (AFn.java:22)

    java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1145)

    java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:615)

    java.lang.Thread.run (Thread.java:744)

nil

user=> (clojure.repl/pst *e)

CompilerException clojure.lang.ArityException: Wrong number of args (3) passed to: core/char--inliner, compiling:(/tmp/form-init9068522213039312274.clj:1:1)

        clojure.lang.Compiler.analyzeSeq (Compiler.java:6651)

        clojure.lang.Compiler.analyze (Compiler.java:6445)

        clojure.lang.Compiler.analyze (Compiler.java:6406)

        clojure.lang.Compiler$BodyExpr$Parser.parse (Compiler.java:5782)

        clojure.lang.Compiler$FnMethod.parse (Compiler.java:5217)

        clojure.lang.Compiler$FnExpr.parse (Compiler.java:3846)

        clojure.lang.Compiler.analyzeSeq (Compiler.java:6642)

        clojure.lang.Compiler.analyze (Compiler.java:6445)

        clojure.lang.Compiler.eval (Compiler.java:6700)

        clojure.lang.Compiler.eval (Compiler.java:6666)

        clojure.core/eval (core.clj:2927)

        clojure.main/repl/read-eval-print--6625/fn--6628 (main.clj:239)

Caused by:

ArityException Wrong number of args (3) passed to: core/char--inliner

        clojure.lang.Compiler.analyzeSeq (Compiler.java:6639)

        clojure.lang.Compiler.analyze (Compiler.java:6445)

        clojure.lang.Compiler.analyze (Compiler.java:6406)

        clojure.lang.Compiler$BodyExpr$Parser.parse (Compiler.java:5782)

        clojure.lang.Compiler$FnMethod.parse (Compiler.java:5217)

        clojure.lang.Compiler$FnExpr.parse (Compiler.java:3846)

nil

The top part of their output is the same, but not the bottom.

If no-one comes up with an explanation, I'll use both until I understand which one is more useful to me, and report back here if I remember (hopefully!)

[Stuart Sierra]

They're just different versions of the same thing, written at different times by different people, that both got merged into Clojure at different times.

Speaking as the original author of clojure.stacktrace, I now think neither one of them should exist. The .printStackTrace method on an exception gives you all the same information and is more reliable.

-S

[mascip]

Thank you Stuart, this is a very useful answer.

Is there any way to access an exception older than *e? 

What happens to me regularly is to mistype (.printStackTrace *e), which makes me lost my previous exception.

-- Pierre Masci

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[Andy Fingerhut]

I know of no way that older exceptions than *e are automatically saved anywhere (unlike the results of previous REPL expressions, of which the last 3 are saved in *1 *2 *3).

When an exception occurs, it is probably much less error-prone to type a short expression like (def e1 *e) to save the exception in e1, even if another exception occurs after that which modifies *e.

Andy

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[mascip]

Saving *e in a def for further investigation, handy :) Cheers