What 28 frames are elided when dividing by zero in the REPL?

Question

scala> 5 / 0
java.lang.ArithmeticException: / by zero
  ... 28 elided

Twenty eight frames elided for a simple arithmetic expression?! What are these frames, why does Scala need that many to do safe division, and why are they being elided in the first place?

Just a guess, wouldn't it make sense that the REPL executing your expression adds some stack levels and would be un-interesting enough to be elided? — Joachim Isaksson, Jun 20 '19 at 19:03
It happens for any exception. ```scala> throw new RuntimeException java.lang.RuntimeException ... 28 elided``` — Alonso del Arte, Oct 12 '20 at 03:34
Though there are ways to get more interesting stack traces ```scala> res2.take(10).toList java.lang.IllegalArgumentException: Dividing -1 by 0 results in an indeterminate number. at fractions.Fraction.dividedBy(Fraction.java:159) at .$anonfun$newtonSqrt$2(:1) at scala.collection.immutable.LazyList$.$anonfun$iterate$2(LazyList.scala:1157) at scala.collection.immutable.LazyList$.$anonfun$iterate$1(LazyList.scala:1156) at scala.collection.immutable.LazyList.scala$collection$immutable$LazyList$$state$lzycompute(LazyList.scala:218) ... 28 elided``` — Alonso del Arte, Oct 12 '20 at 03:48
Got one with 28 and 29 trying to use a Kotlin class from the Scala REPL... — Alonso del Arte, Oct 18 '20 at 04:29

score 7 · Accepted Answer · answered Jun 20 '19 at 19:02

scala> import scala.util.Try
import scala.util.Try

scala> Try(5/0)
res2: scala.util.Try[Int] = Failure(java.lang.ArithmeticException: / by zero)

scala> res2.recover { case e: ArithmeticException => e.printStackTrace }
java.lang.ArithmeticException: / by zero
    at $line8.$read$$iw$$iw$$anonfun$1.apply$mcI$sp(<console>:13)
    at $line8.$read$$iw$$iw$$anonfun$1.apply(<console>:13)
    at $line8.$read$$iw$$iw$$anonfun$1.apply(<console>:13)
    at scala.util.Try$.apply(Try.scala:192)
    at $line8.$read$$iw$$iw$.<init>(<console>:13)
    at $line8.$read$$iw$$iw$.<clinit>(<console>)
    at $line8.$eval$.$print$lzycompute(<console>:7)
    at $line8.$eval$.$print(<console>:6)
    at $line8.$eval.$print(<console>)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:786)
    at scala.tools.nsc.interpreter.IMain$Request.loadAndRun(IMain.scala:1047)
    at scala.tools.nsc.interpreter.IMain$WrappedRequest$$anonfun$loadAndRunReq$1.apply(IMain.scala:638)
    at scala.tools.nsc.interpreter.IMain$WrappedRequest$$anonfun$loadAndRunReq$1.apply(IMain.scala:637)
    at scala.reflect.internal.util.ScalaClassLoader$class.asContext(ScalaClassLoader.scala:31)
    at scala.reflect.internal.util.AbstractFileClassLoader.asContext(AbstractFileClassLoader.scala:19)
    at scala.tools.nsc.interpreter.IMain$WrappedRequest.loadAndRunReq(IMain.scala:637)
    at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:569)
    at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:565)
    at scala.tools.nsc.interpreter.ILoop.interpretStartingWith(ILoop.scala:807)
    at scala.tools.nsc.interpreter.ILoop.command(ILoop.scala:681)
    at scala.tools.nsc.interpreter.ILoop.processLine(ILoop.scala:395)
    at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:415)
    at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply$mcZ$sp(ILoop.scala:923)
    at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:909)
    at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1.apply(ILoop.scala:909)
    at scala.reflect.internal.util.ScalaClassLoader$.savingContextLoader(ScalaClassLoader.scala:97)
    at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:909)
    at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:74)
    at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:87)
    at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:98)
    at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:103)
    at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)
res3: scala.util.Try[AnyVal] = Success(())

The elided lines are basically the REPL's overhead of reading a line, compiling it into a class, and constructing an instance of the class, which is where the code written in the REPL is evaluated.

And it goes without saying that really everything in that stack trace below `scala.util.Try$.apply` is an implementation detail that obscures the part of the stack trace that would be common if you copied into a `main` method and ran it. — Levi Ramsey, Jun 20 '19 at 19:07
Thank you very much for this answer. I was going to ask a more general question, but this answers it. — Alonso del Arte, Oct 12 '20 at 04:01

What 28 frames are elided when dividing by zero in the REPL?

1 Answers1