My original parser (much larger than this minimalist toy example I extracted only to illustrate a point) used parser combinators, was slow, and passed around a lot of contextual information as needed for semantic predicates and swapping out different lexing behavior. There were nested symbol tables, for example. Not all the state was cleanly passed around; some of it was in manually handled global mutable state with homegrown stacks.
So I tried to write a new parser in Parboiled2 using only the value stack.
But there seems to be a bug in Parboiled 2.1.0?
Beginning of the stack trace:
org.parboiled2.ValueStackUnderflowException
at org.parboiled2.ValueStack.pop(ValueStack.scala:104)
at com.franklinchen.StatefulParser.Word(StatefulParser.scala:67)
at com.franklinchen.StatefulParser.Line(StatefulParser.scala:48)
at com.franklinchen.StatefulParser.rec$2(StatefulParser.scala:33)
at com.franklinchen.StatefulParser.Document(StatefulParser.scala:30)
at com.franklinchen.StatefulParser.Start(StatefulParser.scala:22)
at com.franklinchen.StatefulParser$$anonfun$1.apply(StatefulParser.scala:82)
at com.franklinchen.StatefulParser$$anonfun$1.apply(StatefulParser.scala:82)
at org.parboiled2.Parser.runRule$1(Parser.scala:142)
at org.parboiled2.Parser.phase0_initialRun$1(Parser.scala:150)
at org.parboiled2.Parser.__run(Parser.scala:203)
at com.franklinchen.StatefulParser$.delayedEndpoint$com$franklinchen$StatefulParser$1(StatefulParser.scala:82)
at com.franklinchen.StatefulParser$delayedInit$body.apply(StatefulParser.scala:79)
at scala.Function0$class.apply$mcV$sp(Function0.scala:34)
at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:12)
at scala.App$$anonfun$main$1.apply(App.scala:76)
at scala.App$$anonfun$main$1.apply(App.scala:76)
at scala.collection.immutable.List.foreach(List.scala:381)
at scala.collection.generic.TraversableForwarder$class.foreach(TraversableForwarder.scala:35)
at scala.App$class.main(App.scala:76)
at com.franklinchen.StatefulParser$.main(StatefulParser.scala:79)
at com.franklinchen.StatefulParser.main(StatefulParser.scala)
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:497)
at sbt.Run.invokeMain(Run.scala:67)
at sbt.Run.run0(Run.scala:61)
at sbt.Run.sbt$Run$$execute$1(Run.scala:51)
at sbt.Run$$anonfun$run$1.apply$mcV$sp(Run.scala:55)
at sbt.Run$$anonfun$run$1.apply(Run.scala:55)
at sbt.Run$$anonfun$run$1.apply(Run.scala:55)
at sbt.Logger$$anon$4.apply(Logger.scala:85)
at sbt.TrapExit$App.run(TrapExit.scala:248)
at java.lang.Thread.run(Thread.java:745)
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