Explicit unions

[annevk]

@awesomekling mentioned he'd prefer somewhat more explicit union syntax in algorithms as opposed to "null or X", "string-or-null", etc.

It's a little awkward now and then currently, especially with null, so this seems worth considering.

Perhaps something like this:

To do algorithm, given a union { null, string } input, ...

[domenic]

I don't understand the advantages of this. We could try to be more consistent about how we declare nullability, but this kind of non-English syntax feels out of place.