Keep the best of both worlds, go ToJSONObject -> ToJSON as soon as a :@: is formed, but forward the ToJSONObject instance too (so that future :@:-extensions can be made and magically get the ToJSON instance while propagating the ToJSONObject instance)

Add parsing UIDs as a requirement for Record, explain how they propagate along @-chains and make a case-insensitive instance for Work

Propagate Eq and Ord along @ to be able to use composite types as keys (typically, ParagraphRecord defined out of ArticleRecord

Directly implement ToJSON on @ instead of an intermediate ToJSONObject => ToJSON to avoid confusing the compiler

Reverse associativity of '@': we want to enrich metadata on the right of lines, without having to explode existing structures. A paragraph with a class should be just that, and not an article combined to a paragraph number and a class: (Article @ Paragraph) @ Class, not Article @ (Paragraph @ Class)

* Add optparse-applicative parsers for input / output parameters
* Rework metadata types and the way they compose (splitting Article into
  PrimaryKey and Entry)