Why visibility is a string and not a union type?

[Antontelesh]

I'm new to Elm and reading code to understand language and patterns.
For me it seems like making visibility a union type would be better for understanding the code and type safety. Isn't it?

type Visibility
  = Active
  | Completed
  | All

[jwmerrill]

I tried making this change: master...jwmerrill:visibility-type

It mostly worked out nicely. The compiler told me everything I needed to do after I created the Visibility type and changed the type of Model.

However, you can't currently serialize a Union Type directly through a port, so if you make this change, the serialization to localStorage gets more complicated. I just ripped that feature out in my branch, so it isn't suitable for a PR. I think this won't be easy until elm/compiler#490 is solved.

[Antontelesh]

@jwmerrill Thank you for this investigation and explanation. Now it is clear for me.