Union types

[brendanzab]

OpenType has lots of union types! We should have a nice way of describing them.

TODO

• Add concrete syntax
• Use backtracking and ordered choice
• Identify common prefixes, without backtracking
• Compile to tagged union types in the host language

[brendanzab]

I wonder if we could have something like this:

union Foo (param : T) & Bar param {
    Foo0,
    Foo1,
};

This would ensure that each variant properly intersects with the given prefix.

[brendanzab]

Perhaps this might be clearer:

union Foo & FooUnknown {
    Foo0,
    Foo1,
    FooUnknown,
};

struct Foo0 {
    version : U16Be == 0,
    data : U32Be,
};

struct Foo0 {
    version : U16Be == 1,
    data : F64Be,
};

struct FooUnknown {
    version : U16Be,
};

[brendanzab]

I dunno though 🤷‍♂️