Cannot define one-element static array of string

This doesn't work:

```
main> EVAL ["foo"];
request failed: E0007: Cannot process a statement: {"error":"expression is not foldable: [\"foo\"]","statement":"EVAL [\"foo\"]"}
```

However this works:

```
main> EVAL ["foo",];
["foo"]

main> EVAL ["foo", "bar"];
["foo","bar"]

main> EVAL ["foo"::string];
["foo"]

main> EVAL [1];
[1]
```