Your First Nenu Program

The runnable receives its Request and Response contracts from App Marché metadata.
It fetches the room and payer, constructs an Expense, saves it, and returns Response.
This first example is intentionally complete; later pages explain every line separately.

Goal And Contracts

The runnable creates one expense for the room. Its metadata provides a Request with room_id, payer_id, title, and amount. Its Response contains the saved expense. Do not declare type Request or type Response in source.

Input	Type	Meaning
`request.room_id`	`string`	The one room receiving the expense.
`request.payer_id`	`string`	The existing platform user who paid.
`request.title`	`string`	A short description such as Internet.
`request.amount`	`number`	The amount paid.

Complete Runnable

apis/expenses/create.api.nenu

1need {2  room = Room(request.room_id)3  payer = User(request.payer_id)4}56Expense expense = Expense {7  room_id: room.id8  payer9  title: request.title10  amount: request.amount11  note: ?12  receipt: ?13  status: ExpenseStatus.Open14}1516save(expense)17return Response { expense }

Walkthrough

need fetches the existing Room and platform-provided User before ordinary runnable statements execute.
Expense expense declares a local named expense with an explicit entity type.
Expense { ... } constructs a value. room_id: room.id is an explicit field expression, while bare payer is shorthand for payer: payer.
save(expense) persists the new record. Save always uses parentheses.
return Response { expense } satisfies the metadata-defined response contract on the successful path.

Expected Result

Given a valid room, payer, title, and amount, the runnable creates one durable Expense and returns it in the expense response field. A missing required fetch or an incompatible request field is a hard failure rather than an absent partial result.

Common Mistakes

Wrong	Correct	Reason
Declare the platform User type locally	`User(request.payer_id)`	User is supplied by the platform.
`new Expense { ... }`	`Expense { ... }`	Nenu has no new keyword.
`needs { ... }`	`need { ... }`	The keyword is singular.
`save expense`	`save(expense)`	Save requires parentheses.
`respond { expense }`	`return Response { expense }`	The old respond statement was removed.

Continue Learning

Files And Declarations Understand where definitions and runnable statements belong.Entities Learn how Room and Expense are defined and validated.API Runnables Learn the complete Request-to-Response workflow contract.