Validation of empty lists

[robertodr]

type_matches([], 'List[T]') is true for any underlying type T. Should type_matches throw on empty lists?

[bast]

For me it is fine if that function returns True.

If we do not allow empty lists, I think this should be caught one level up.

[robertodr]

Turns out tests for the grammar were not looking at this edge case.

[stigrj]

Somewhat related:
At least in the getkw grammar, an input list with a single entry of type T is translated to a raw type T in the processed JSON, e.i.

double_array = [1.0]

translates into

{
  "double_array" : 1.0
}

This behavior is not wanted if you have lists of unknown size.

[robertodr]

Dang! Not good, not good at all. I'll add tests and see how this can be fixed.

[robertodr]

I have asked a question on StackOverflow, because all my attempts at raising meaningful exceptions on empty lists have been unsuccessful. Here is the question, which also includes an example: https://stackoverflow.com/questions/55187629/pyparsing-raise-exception-on-emtpy-delimitedlist