Custom "enum" types with a custom type provider

[davenewza]

In our language context we have dynamic enum-like types. For example, a query might be:

person.status == Status.Married

The enum type Status acts like how we typically understand enum types - it is defined with a set of options. For example, Status.Married or Status.Single would be the defined values.

I'm unsure exactly how to define this with the custom type provider. I've achieved a working solution by defining the enum type as a constant object type and its values as opaque types.

Could this be considered a reasonable approach?

We define all our types dynamically at runtime (and not using Go structs or proto definitions). The below Gist very simply illustrates how I have achieved this:

https://gist.github.com/davenewza/81ebf3f30b0fde94419d9ba090327a5c

What isn't so great about this approach is:

• the issue returned on an invalid expression person.status == Status.wrong is undefined field 'wrong' but enums don't really have fields.
• the issue returned on an invalid expression person.status == Status is found no matching overload for '_==_' applied to '(Status, StatusEnumDefinition)' whereas I might prefer something like value expected for Status
• types.NewNullableType() doesn't seem to let define nullable fields on opaque types