Reproducing the Examples

Every answer in this book was produced by the law command-line tool, either from a case package — a small package that holds fictional files, each with its facts and legal date, and imports the canons whose rules apply — or from the declared scenarios of the Wohngeld canon itself. The rules are never copied into the case.

What you need

• The law command-line tool, version 0.2.2 or later (npm i -g @arxo/cli), executing law.core/0.2.11. The chapters say which version recorded each table: on 12 October 2026, law 0.1.12 in a checkout of the Arxo repository. The reproduction kit below was checked the same day with the released law 0.2.2: the same amounts and statuses.
• The reproduction kit of this book: two public repositories.
  • the canons, github.com/arxohq/arxo-wohngeld: the three German canons, each with its sources, pinned legal texts and scenarios, and a registry from which the case packages install them;
  • the examples, github.com/arxohq/law-as-code-germany-examples: the case packages and the saved answers of Chapter 9.

Getting the kit

r=https://github.com/arxohq
git clone $r/arxo-wohngeld.git
git clone $r/law-as-code-germany-examples.git examples

The case package of the chapters’ commands, <case package>, is examples/familie-weimar. The canon, <canon>, is the folder arxo-wohngeld/packages/de.social.wohngeld: its dependencies are pinned inside it, so there is nothing to install.

law install never picks versions: it restores exactly what law.lock pins and checks every hash. In a checkout of the Arxo repository the same package and canon are corpus/laws/de/wohngeld/examples/familie-weimar and corpus/laws/de/wohngeld.

The case package

All the files of the Vogts and of the excluded woman are in one case package, familie-weimar — the <case package> of the chapters’ commands. It holds four files and six saved questions.

The questions are JSON files in queries/:

One fact changed

The variations of Chapters 2, 3, 4 and 8 — the Vogts’ case with one fact changed — are five cases of a second case package of the kit, familie-weimar-varianten. Its questions collect the value (collect-y, collect-m, collect-w, collect-n for Y, M, the Wohngeld and the number of members).

The canon’s scenarios

The other answers are scenarios of the Wohngeld canon — the <canon> of the chapters’ commands:

Asking a question

Work in the case package directory — from the folder where you cloned the kit:

cd examples/familie-weimar
law install --registry arxo=../../arxo-wohngeld/registry
law ask . --case Familie2025 \
    --query-json queries/wohngeld-485.json --out "$(mktemp -d)"

--case names the file, --query-json the question; --out saves the full answer — status, proof and fingerprints — in a directory.

Running the scenarios

In the canon folder, arxo-wohngeld/packages/de.social.wohngeld:

law test . --file tests/bmwsb-2025.lawtest

Each line reports a scenario as passed or failed, and a total. On 12 October 2026 the 2023 suite passed 9 of 9, the 2025 suite 10 of 10, the edition suite 6 of 6, the suite of missing and conflicting facts 7 of 7, and the suite of exclusions and judgments 16 of 16; in arxo-wohngeld, with the released law 0.2.2, all 87 scenarios of the canon passed.

Replaying a saved answer

The kit keeps the two answers of Chapter 9 in familie-weimar/runs/. Replay one in a copy:

d="$(mktemp -d)"
cp -R runs/familie-2025 "$d"
law eval "$d/familie-2025"
shasum -a 256 runs/familie-2025/result.json \
    "$d/familie-2025/result.json"

law eval evaluates the saved answer again — without the source files or a rebuild — and must give the same bytes. Compare the program and case fingerprints in the manifest and the fingerprint of result.json in the original and the replay: if they match, the same program gave the same answer to the same case. That shows repeatability, not legal correctness — Chapter 9 explains the difference.

The saved answers and their fingerprints, recorded on 12 October 2026; each replay was byte for byte identical:

If your answer differs

Check, in this order: the version of law; the legal date and the facts of the file; the editions and annex rows the canon pins. A later edition of a text, or a corrected fact, gives a new answer to a new question — not a failed reproduction of the old one.