Document editorial workflow with a typed (sum-type) state machine

document_review.cell

// Document editorial workflow with a typed (sum-type) state machine.
// A draft is submitted for review; a reviewer either requests changes
// (back to draft) or approves; approved documents are published. The
// changes-requested loop is bounded by reaching `published` or `archived`
// from every state, so liveness holds.

cell type DocState {
    variants { Draft  InReview  Approved  Published  Archived }
}

cell Editorial {
    face {
        signal create(id: String) -> String
        signal submit(id: String) -> String
        signal request_changes(id: String) -> String
        signal approve_doc(id: String) -> String
        signal publish_doc(id: String) -> String
        signal archive(id: String) -> String
        signal status(id: String) -> String
    }

    state doc: DocState {
        initial: Draft
        Draft     -> InReview
        InReview  -> Draft
        InReview  -> Approved
        Approved  -> Published
        *         -> Archived
    }

    on create(id: String)          { return get_status(id) }
    on submit(id: String)          { transition(id, InReview)   return get_status(id) }
    on request_changes(id: String) { transition(id, Draft)      return get_status(id) }
    on approve_doc(id: String)         { transition(id, Approved)   return get_status(id) }
    on publish_doc(id: String)         { transition(id, Published)  return get_status(id) }
    on archive(id: String)         { transition(id, Archived)   return get_status(id) }
    on status(id: String)          { return get_status(id) }
}

cell test EditorialTests {
    rules {
        // submit -> request changes -> resubmit -> approve -> publish
        assert create("d1") == "Draft"
        assert submit("d1") == "InReview"
        assert request_changes("d1") == "Draft"
        assert submit("d1") == "InReview"
        assert approve_doc("d1") == "Approved"
        assert publish_doc("d1") == "Published"

        // any document can be archived (the * arrow), here from Draft
        assert archive("d2") == "Archived"

        // illegal: cannot publish straight from Draft
        assert_fails publish_doc("d3")
        // illegal: cannot approve a document that isn't in review
        assert_fails approve_doc("d4")
    }
}