The form and the agent tool invoke the same business operation.
That is Canlang's syntactic bet: reduce the amount of application structure an agent must invent and repeat. Static types, explicit authority checks and executable examples supply the verification overlap. The language targets tasks, approvals, bookings, invoicing and similar operational software; its [requirements](https://github.com/veighnsche/canlang/blob/main/docs/specification/REQUIREMENTS.md) prioritise economical generation and maintenance without claiming a measured cost advantage. ## What it looks like. Each package organises code into three sections: `Given` declares data and rules, `When` declares operations, and `Then` declares presentation. Here, a reviewer can approve a submitted expense, but never their own. This excerpt adapts [ExpenseFlow](https://github.com/veighnsche/canlang/blob/main/examples/ExpenseFlow.can); the app header and create/submit workflow are omitted to focus on approval.Given role reviewer Expense { purpose:text trim max=300, amount:money, submitted_by:user server=actor, status:enum(draft,submitted,approved)=draft, decided_by:user?, decided_at:datetime? } policy Expense read=members where=row.submitted_by==actor policy Expense read=reviewer invariant Expense: row.amount.minor>0 lock Expense fields=purpose,amount,submitted_by when=row.status!=draft lock Expense fields=status,decided_by,decided_at when=row.status==approved fixture pending=Expense {purpose="Travel",amount=money(25,"EUR"), submitted_by=other,status=submitted} When # Approve a submitted expense belonging to another teammate. scenario approve(expense:Expense) by=reviewer require expense.status==submitted and expense.submitted_by!=actor do set expense {status=approved,decided_by=actor,decided_at=now} examples expense=pending as,expense.status,expense.submitted_by -> expense.status,expense.decided_by reviewer,submitted,other -> approved,self reviewer,draft,other -> error(rule_failed) members,submitted,other -> error(forbidden) reviewer,submitted,self -> error(rule_failed) Then page / title="Expenses" list Expense order=-created text row.purpose,row.amount,row.status form approve arguments={expense=row}
Four example rows test valid approval, invalid state, missing role authority and self-approval. The form binds the same operation to each listed expense; locks freeze submitted details and the final decision.