One way that error messages could be more helpful
Opening this by request of @GreyCat. Last night I wasted a lot of time because in an earlier version of this line: https://github.com/Deep-Symmetry/beat-link/blob/5da596c526768a3f6df40d044754845f6397dc67/kaitai/pdb.ksy#L211 I had forgotten that the `ksc` expression language uses `and` for conjoining boolean expressions, rather than `&&` like most C-derived languages I generally use, so I had `&&` instead of the `and` there. Unfortunately, the error message I received was:

    End:1:35 ..."&& (num_ro"

That gave me no context whatsoever, not even the line number. It would have been far more helpful to say something like:

    Unrecognized token "&&" at line 211, column 44.

That would have at least sent me to the manual to look for the right thing. Since this is probably a common mistake, you could even be extra nice and say something like:

    Unrecognized token "&&" at line 211, column 44, did you mean "and"?

Something similar could be offered for `||` and `or`.

Even looking at the exception, now that I know that trick, did not help:
```
Exception in thread "main" io.kaitai.struct.exprlang.Expressions$ParseException: End:1:35 ..."&& (num_ro"
	at io.kaitai.struct.exprlang.Expressions$.realParse(Expressions.scala:178)
	at io.kaitai.struct.exprlang.Expressions$.parse(Expressions.scala:170)
	at io.kaitai.struct.format.InstanceSpec$.$anonfun$fromYaml$1(InstanceSpec.scala:44)
	at scala.Option.map(Option.scala:146)
	at io.kaitai.struct.format.InstanceSpec$.fromYaml(InstanceSpec.scala:44)
	at io.kaitai.struct.format.ClassSpec$.$anonfun$instancesFromYaml$1(ClassSpec.scala:211)
	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
	at scala.collection.MapLike$MappedValues.$anonfun$foreach$3(MapLike.scala:253)
	at scala.collection.TraversableLike$WithFilter.$anonfun$foreach$1(TraversableLike.scala:789)
	at scala.collection.immutable.Map$Map3.foreach(Map.scala:176)
	at scala.collection.TraversableLike$WithFilter.foreach(TraversableLike.scala:788)
	at scala.collection.MapLike$MappedValues.foreach(MapLike.scala:253)
	at scala.collection.TraversableLike.map(TraversableLike.scala:234)
	at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
	at scala.collection.AbstractTraversable.map(Traversable.scala:104)
	at io.kaitai.struct.format.ClassSpec$.instancesFromYaml(ClassSpec.scala:207)
	at io.kaitai.struct.format.ClassSpec$.fromYaml(ClassSpec.scala:107)
	at io.kaitai.struct.format.ClassSpec$.$anonfun$typesFromYaml$1(ClassSpec.scala:201)
	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
	at scala.collection.immutable.HashMap$HashMap1.foreach(HashMap.scala:231)
	at scala.collection.immutable.HashMap$HashTrieMap.foreach(HashMap.scala:462)
	at scala.collection.TraversableLike.map(TraversableLike.scala:234)
	at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
	at scala.collection.AbstractTraversable.map(Traversable.scala:104)
	at io.kaitai.struct.format.ClassSpec$.typesFromYaml(ClassSpec.scala:199)
	at io.kaitai.struct.format.ClassSpec$.fromYaml(ClassSpec.scala:103)
	at io.kaitai.struct.format.ClassSpec$.fromYaml(ClassSpec.scala:224)
	at io.kaitai.struct.formats.JavaKSYParser$.fileNameToSpec(JavaKSYParser.scala:29)
	at io.kaitai.struct.formats.JavaKSYParser$.localFileToSpecs(JavaKSYParser.scala:18)
	at io.kaitai.struct.JavaMain.compileOneInput(JavaMain.scala:237)
	at io.kaitai.struct.JavaMain.$anonfun$run$1(JavaMain.scala:212)
	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
	at scala.collection.immutable.List.foreach(List.scala:389)
	at scala.collection.TraversableLike.map(TraversableLike.scala:234)
	at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
	at scala.collection.immutable.List.map(List.scala:295)
	at io.kaitai.struct.JavaMain.run(JavaMain.scala:210)
	at io.kaitai.struct.JavaMain$.main(JavaMain.scala:201)
	at io.kaitai.struct.JavaMain.main(JavaMain.scala)
```

In the end, I spent a long time trying to separate the expression into simpler sub-expressions using additional parse instances to try to figure out what was going on, and eventually slapped my forehead and vented in the Gitter chat. Hopefully we can spare future adopters such fun. 😄 