Very few languages let you have multiple versions of the same package in one project; fewer let you use functions from both versions together; and even fewer make this easy!

This is something that would be enabled with hash identifiers and no modules:

    let foo_1 = universe.mega_corp.finance_dept.team_alpha@v1.0.0.foo
    let foo_2 = universe.mega_corp.finance_dept.team_alpha@v2.0.0.foo

    let compare_old_new_foo(x) =
      foo_2(x) - foo_1(x)

There would be a corresponding lock-file to make this reproducible:

    {
      "universe.mega_corp.finance_dept.team_alpha": {
        "v1.0.0": "aabbcc",
        "v2.0.0": "xxyyzz"
      }
    }

I think this is pretty neat!