Allow accessing nested VariantLists

[stasm]

There is currently no way to access variants nested in other variants:

-brand-name = {
    *[singular] {
        *[nominative] Thing
        [genitive] Thing's
    }
    [plural] {
        *[nominative] Things
        [genitive] Things'
    }
}

# Nested VariantExpressions (currently syntax errors)
A = {-brand-name[singular][genitive]}
B = {-brand-name[singular, genitive]}

If #176 is accepted and if parameterized terms replace variant lists, we might not need this at all. Otherwise, I would suggest to use the same syntax as will be used for list selectors (#4). My comment in #4 (comment) has the rationale for my preference for option B.

[stasm]

For both A and B we should find an answer to the question no. 6 from #176 (comment). Should be it possible to invoke the default value of an upper level and pass a specific key to the nested VariantList? In pseudocode:

# Either a new Fluent symbol NONE,
# or just leverage the fact that no variant has key == NONE.
X = {-brand-name[NONE, genitive]}
# Empty placeable could mean "null"
X = {-brand-name[{}, genitive]}
# Implicit "null"
X = {-brand-name[, genitive]}

I don't like any of these solutions. I think we should encourage explicit syntax, especially in areas which are already quite complex. Terms with variant lists definitely qualify as such in my book. I'm OK with answering No to the original question, and requiring all keys to be always present:

B = {-brand-name[singular, genitive]}

[stasm]

Parameterized terms (#176) supersede variant lists, making this issue obsolete. I filed #204 to remove variant lists from the syntax.

[mariusrak]

Hi, can you please explain how can I use parametrized terms to achieve what variant lists would allow? Thanks.

[artlung]

@mariusrak I suspect this is not a great place to ask a question like that. But I suspect looking at https://projectfluent.org/fluent/guide/selectors.html will get you started at how to create ftl with variants. Also if I had a question I might feel inclined to ask on StackOverflow with a project-fluent tag. https://stackoverflow.com/questions/tagged/project-fluent