Allow ..Nothing to resolve to Nothing

[JaroslavTulach]

Pull Request Description

Fixes #9738 in a different way than #9743.

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• All code follows the
  Java,
• All code has been tested:
  • Unit tests have been written where possible.

[JaroslavTulach]

Benchmarks run scheduled.

[radeusgd]

Looks ok but I think I missed why we want to allow that?

[JaroslavTulach]

Addresses #9738. The

• Autoscoped constructors #9190

introduced the ..Constructor syntax. In case of singletons like Nothing or Pavel (in the example below), the type is de-factor its own constructor. Thus it make sense to support ..Nothing or ..Pavel syntax of autoscoped constructors.

[Akirathan]

Is this supposed to work also for other types than Nothing? For example:

from Standard.Base import Date

main =
  ..Date == Date
```?

[JaroslavTulach]

from Standard.Base import Date

main =
  ..Date == Date

This example yields False. Probably because == doesn't force conversion of unresolved constructor to real constructor. If I modify your code to:

from Standard.Base import Date

materialize (d:Date) = d

main =
  d = materialize ..Date
  d == Date

Then one gets Cannot find constructor ..Date among Date. It is all supposed to work only for singletons. Following program returns True:

type Pavel


materialize (d:Pavel) = d

main =
  d = materialize ..Pavel
  d == Pavel

[JaroslavTulach]

Benchmarks seem to be unaffected by this change: