Having arrays indexed by other things than just integers could be useful:

* Enum
* (Maybe) 1-byte characters / ASCII characters
    - Or perhaps allow integers to be subtyped into non-integer compatible
      types (but still "word-sized" and "ordinal").

Can lists and maps be unified?
------------------------------

A more extreme variant could be to have only different types of maps:

* Ordering:
    - by index
    - by insertion order
    - unordered
* Sparseness:
    - all indices are present
    - a 0-based range is present
    - an arbitrary range is present
    - sparse map with word-sized indices
    - sparse map with arbitrary-sized indices
* Deletion behavior
    - elements above are moved down
    - a hole is created

Ordering by index, 0-based range and move-down-on-delete is equivalent to a
list.