Make sturctures with default values irrepresentable, use Maybe to demonstrate absence of value rather than a struct with default nonsense.

[cognivore]

Why?

We're using a neat hack to create default temporary structures when we don't have enough information to create a filled one.

For example, have a look at code in lib/zhr_devs/submissions/aggregates/submission.ex:57

It's not a good design. If something doesn't make sense to have a default value of type a, then either that field of the thing has to be Nothing or Just a, or, sometimes, the whole thing should be Maybe (Thing a)

How

• Tweak Maybe in Algae so that it preserves the underlying type information (see Uptight.Result.sum(e, a)). Ensure backwards-compatibility.
• Replace structures and field with Maybes in zhr_devs