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POWhy are Clojure stacktraces so long?
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copied!<p>I've written some toy interpreters/compilers in the past, so I associate stacktraces referencing lines in compiler source files with compiler bugs.</p> <p>If I add the following bad function definition to my compojure project:</p> <pre><code>(defn dodgy-map [] {:1 :2 :3}) </code></pre> <p>Lein refuses to start:</p> <pre><code>$ lein ring server-headless Exception in thread "main" java.lang.RuntimeException: Map literal must contain an even number of forms, compiling:(one_man_wiki/views.clj:19) at clojure.lang.Compiler.load(Compiler.java:6958) at clojure.lang.RT.loadResourceScript(RT.java:359) at clojure.lang.RT.loadResourceScript(RT.java:350) at clojure.lang.RT.load(RT.java:429) at clojure.lang.RT.load(RT.java:400) at clojure.core$load$fn__4890.invoke(core.clj:5415) at clojure.core$load.doInvoke(core.clj:5414) at clojure.lang.RestFn.invoke(RestFn.java:408) at clojure.core$load_one.invoke(core.clj:5227) at clojure.core$load_lib.doInvoke(core.clj:5264) at clojure.lang.RestFn.applyTo(RestFn.java:142) at clojure.core$apply.invoke(core.clj:603) at clojure.core$load_libs.doInvoke(core.clj:5298) at clojure.lang.RestFn.applyTo(RestFn.java:137) at clojure.core$apply.invoke(core.clj:603) at clojure.core$require.doInvoke(core.clj:5381) at clojure.lang.RestFn.invoke(RestFn.java:457) at one_man_wiki.handler$eval1564$loading__4784__auto____1565.invoke(handler.clj:1) at one_man_wiki.handler$eval1564.invoke(handler.clj:1) at clojure.lang.Compiler.eval(Compiler.java:6511) at clojure.lang.Compiler.eval(Compiler.java:6501) at clojure.lang.Compiler.load(Compiler.java:6952) at clojure.lang.RT.loadResourceScript(RT.java:359) at clojure.lang.RT.loadResourceScript(RT.java:350) at clojure.lang.RT.load(RT.java:429) at clojure.lang.RT.load(RT.java:400) at clojure.core$load$fn__4890.invoke(core.clj:5415) at clojure.core$load.doInvoke(core.clj:5414) at clojure.lang.RestFn.invoke(RestFn.java:408) at clojure.core$load_one.invoke(core.clj:5227) at clojure.core$load_lib.doInvoke(core.clj:5264) at clojure.lang.RestFn.applyTo(RestFn.java:142) at clojure.core$apply.invoke(core.clj:603) at clojure.core$load_libs.doInvoke(core.clj:5298) at clojure.lang.RestFn.applyTo(RestFn.java:137) at clojure.core$apply.invoke(core.clj:603) at clojure.core$require.doInvoke(core.clj:5381) at clojure.lang.RestFn.invoke(RestFn.java:421) at user$eval1.invoke(NO_SOURCE_FILE:1) at clojure.lang.Compiler.eval(Compiler.java:6511) at clojure.lang.Compiler.eval(Compiler.java:6500) at clojure.lang.Compiler.eval(Compiler.java:6477) at clojure.core$eval.invoke(core.clj:2797) at clojure.main$eval_opt.invoke(main.clj:297) at clojure.main$initialize.invoke(main.clj:316) at clojure.main$null_opt.invoke(main.clj:349) at clojure.main$main.doInvoke(main.clj:427) at clojure.lang.RestFn.invoke(RestFn.java:421) at clojure.lang.Var.invoke(Var.java:419) at clojure.lang.AFn.applyToHelper(AFn.java:163) at clojure.lang.Var.applyTo(Var.java:532) at clojure.main.main(main.java:37) Caused by: java.lang.RuntimeException: Map literal must contain an even number of forms at clojure.lang.Util.runtimeException(Util.java:170) at clojure.lang.LispReader$MapReader.invoke(LispReader.java:1071) at clojure.lang.LispReader.readDelimitedList(LispReader.java:1126) at clojure.lang.LispReader$ListReader.invoke(LispReader.java:962) at clojure.lang.LispReader.read(LispReader.java:180) at clojure.lang.Compiler.load(Compiler.java:6949) ... 51 more </code></pre> <p>If I reference a variable that doesn't exist:</p> <pre><code>(defn no-such-variable [] i-dont-exist) </code></pre> <p>I get an equally ginormous traceback:</p> <pre><code>Exception in thread "main" java.lang.RuntimeException: Unable to resolve symbol: i-dont-exist in this context, compiling:(one_man_wiki/views.clj:18) at clojure.lang.Compiler.analyze(Compiler.java:6281) at clojure.lang.Compiler.analyze(Compiler.java:6223) at clojure.lang.Compiler$BodyExpr$Parser.parse(Compiler.java:5618) at clojure.lang.Compiler$FnMethod.parse(Compiler.java:5054) at clojure.lang.Compiler$FnExpr.parse(Compiler.java:3674) at clojure.lang.Compiler.analyzeSeq(Compiler.java:6453) at clojure.lang.Compiler.analyze(Compiler.java:6262) at clojure.lang.Compiler.analyzeSeq(Compiler.java:6443) at clojure.lang.Compiler.analyze(Compiler.java:6262) at clojure.lang.Compiler.access$100(Compiler.java:37) at clojure.lang.Compiler$DefExpr$Parser.parse(Compiler.java:518) at clojure.lang.Compiler.analyzeSeq(Compiler.java:6455) at clojure.lang.Compiler.analyze(Compiler.java:6262) at clojure.lang.Compiler.analyze(Compiler.java:6223) at clojure.lang.Compiler.eval(Compiler.java:6515) at clojure.lang.Compiler.load(Compiler.java:6952) at clojure.lang.RT.loadResourceScript(RT.java:359) at clojure.lang.RT.loadResourceScript(RT.java:350) at clojure.lang.RT.load(RT.java:429) at clojure.lang.RT.load(RT.java:400) at clojure.core$load$fn__4890.invoke(core.clj:5415) at clojure.core$load.doInvoke(core.clj:5414) at clojure.lang.RestFn.invoke(RestFn.java:408) at clojure.core$load_one.invoke(core.clj:5227) at clojure.core$load_lib.doInvoke(core.clj:5264) at clojure.lang.RestFn.applyTo(RestFn.java:142) at clojure.core$apply.invoke(core.clj:603) at clojure.core$load_libs.doInvoke(core.clj:5298) at clojure.lang.RestFn.applyTo(RestFn.java:137) at clojure.core$apply.invoke(core.clj:603) at clojure.core$require.doInvoke(core.clj:5381) at clojure.lang.RestFn.invoke(RestFn.java:457) at one_man_wiki.handler$eval1564$loading__4784__auto____1565.invoke(handler.clj:1) at one_man_wiki.handler$eval1564.invoke(handler.clj:1) at clojure.lang.Compiler.eval(Compiler.java:6511) at clojure.lang.Compiler.eval(Compiler.java:6501) at clojure.lang.Compiler.load(Compiler.java:6952) at clojure.lang.RT.loadResourceScript(RT.java:359) at clojure.lang.RT.loadResourceScript(RT.java:350) at clojure.lang.RT.load(RT.java:429) at clojure.lang.RT.load(RT.java:400) at clojure.core$load$fn__4890.invoke(core.clj:5415) at clojure.core$load.doInvoke(core.clj:5414) at clojure.lang.RestFn.invoke(RestFn.java:408) at clojure.core$load_one.invoke(core.clj:5227) at clojure.core$load_lib.doInvoke(core.clj:5264) at clojure.lang.RestFn.applyTo(RestFn.java:142) at clojure.core$apply.invoke(core.clj:603) at clojure.core$load_libs.doInvoke(core.clj:5298) at clojure.lang.RestFn.applyTo(RestFn.java:137) at clojure.core$apply.invoke(core.clj:603) at clojure.core$require.doInvoke(core.clj:5381) at clojure.lang.RestFn.invoke(RestFn.java:421) at user$eval1.invoke(NO_SOURCE_FILE:1) at clojure.lang.Compiler.eval(Compiler.java:6511) at clojure.lang.Compiler.eval(Compiler.java:6500) at clojure.lang.Compiler.eval(Compiler.java:6477) at clojure.core$eval.invoke(core.clj:2797) at clojure.main$eval_opt.invoke(main.clj:297) at clojure.main$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) Caused by: java.lang.RuntimeException: Unable to resolve symbol: i-dont-exist in this context at clojure.lang.Util.runtimeException(Util.java:170) at clojure.lang.Compiler.resolveIn(Compiler.java:6766) at clojure.lang.Compiler.resolve(Compiler.java:6710) at clojure.lang.Compiler.analyzeSymbol(Compiler.java:6671) at clojure.lang.Compiler.analyze(Compiler.java:6244) ... 66 more </code></pre> <p>Why doesn't the Clojure compiler raise a <code>ClojureSyntaxError</code> and a <code>ClojureNameError</code> that could be caught at the top level and a simple error shown? These are common developer errors during development.</p> <p>If the long tracebacks are useful in some circumstances, why are they truncated?</p> <p><strong>Edit</strong>: What I'm looking for in an answer:</p> <ol> <li>Are there situations (some metaprogramming with Java interop perhaps?) when getting a traceback referencing clojure.lang is useful?</li> <li>(Related) Are there any technical constraints preventing adding a <code>ClojureSyntaxError</code> as I described above? Is it worth me opening an issue on the Clojure bug tracker? (update: I've <a href="http://dev.clojure.org/jira/browse/CLJ-1155" rel="noreferrer">opened CLJ-1155</a>)</li> <li>How do experience Clojure programmers read these tracebacks? Are there tools to help? Does everyone use clj-stacktrace?</li> </ol>

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