| Payments approval — a whole service in one file: a ledger that cannot overdraw, a payment lifecycle the verifier proves, an HTTP API that maps error kinds to status codes, and tests that run offline | 165 | a state machine, a memory invariant, HTTP routes, match, try / catch, require / fail, several cells, a whole verified service |
| Warehouse reservations — two cells: a stock ledger with hard bounds and a reservation lifecycle with a supervisor guard, behind one HTTP router | 187 | a state machine, a memory invariant, HTTP routes, match, try / catch, guard blocks, require / fail, several cells, a whole verified service |
| Mini blog API with tag filtering. Posts carry a list of tags; | 61 | HTTP routes, pipes (|>), match, lambdas |
| Form handler with server-side validation | 54 | HTTP routes, match |
| Counter API: a persistent integer counter exposed over HTTP | 68 | HTTP routes, match |
| Feature-flag service: toggle named flags on/off, query state, list all | 61 | HTTP routes, match |
| Guestbook: append-only signed entries, rendered as a small HTML page | 66 | HTTP routes, match |
| Key-value store API with namespaced keys and a bulk export endpoint | 65 | HTTP routes, match |
| Leaderboard API: submit a score, get the ranked top-N | 86 | HTTP routes, pipes (|>), match |
| Metrics / health endpoint. Every request bumps a request counter; | 63 | HTTP routes, match |
| CRUD JSON API over a persistent Map: notes with title + body | 77 | HTTP routes, match |
| Paginated product list: GET /products?page=N&size=M slices a stored list | 57 | HTTP routes, match |
| Voting / poll API: fixed options, one counter per option, results sorted | 63 | HTTP routes, pipes (|>), match, lambdas |
| Session/login toy: POST /login issues a token, GET /me/<token> returns the user, POST /logout invalidates it | 58 | HTTP routes, match |
| Multi-page static site: home, about, and a dynamic greeting route | 42 | HTTP routes, match |
| Todo service backed by a typed state machine (sum type TodoStatus) | 82 | a state machine, a sum type, HTTP routes, match |
| URL shortener: POST a long URL, get a short code; GET the code redirects | 75 | HTTP routes, match |
| Webhook receiver + event log. POST /hook/<source> appends an event; | 71 | HTTP routes, pipes (|>), match, lambdas |