Every function says why it exists. Errors are data, not explosions.
The distinctive move is the breadth of what ships inside one binary. A `.pact` file declares `app Notes { port: 8080, db: "sqlite://notes.db" }` and `pact run` brings up an HTTP server with SSE streaming, SQLite in WAL mode, JWT auth, a structured logger, and a built-in MCP server — no dependencies, no ORM, tables auto-created from struct fields. This is close to Aver in design DNA (declared intent + declared effects + colocated checks), but where Aver lifts verify blocks into Lean 4 and Dafny, Pact spends its complexity budget on the runtime an agent will actually drive. ## What it looks like.intent "create a new user with default Viewer role"
fn create_user(data: NewUser) -> User or BadRequest
needs db, time, rng
{
let existing: User = find_by_email(data.email)
return BadRequest { message: "Email already taken" } if existing != nothing
let user: User = {
id: rng.uuid(),
email: data.email,
role: "Viewer",
active: true,
created_at: time.now(),
}
db.insert("users", user)
}
An intent line, an effect list, and a sum-typed return — all in the signature before the body.