Parsing of recursive array literals

This code:

```scheme
(write '(1 2 #0=#(1 2 #0#)))
```

Prints:

```scheme
(1 2 #(1 2 #))
```

On the first type it threw an error about expecting parenthesis but `#` found. I was not able to repeat this error.

`DatumReference` is an internal value of the parser, and it should never be exposed.

Start by running the Scheme example in the issue and tracing the parser's handling of recursive array literals and DatumReference values. Done means the expression parses and prints without exposing the internal DatumReference value, while avoiding the reported unexpected EOF error.

Written by the indexing model from the issue text.