Structured specs as the new abstraction level for building with AI.

model orders implements sales {

  module orders {

    struct Money {
      schema {
        amount:   number
        currency: string
      }
    }

    struct OrderLine {
      schema {
        sku:       string
        quantity:  number
        unitPrice: Money
      }
    }

    struct Order {
      schema {
        id:     string
        lines:  vector<OrderLine>
        total:  Money
        status: string
      }

      // named conditions over the data,
      // in the domain's own language
      state {
        "a draft order"       : _.status = "draft"
        "a shipped order"     : _.status = "shipped"
        "a cancelled order"   : _.status = "cancelled"
        "a cancellable order" : _.status in { "draft", "confirmed" }
      }
    }

    global orderBook: vector<Order> = []

    operation findOrder(orderId: string): Order
      errors { UnknownOrder }
      reads { orderBook }

    operation cancelOrder(orderId: string): Order
      errors {
        UnknownOrder
        NotCancellable(status: string)
      }
      depends on { findOrder }
      writes { orderBook }
      implements sales.CancelOrder

    // right state in, right state out:
    // examples speak the states' language
    example "cancel while still open" {
      given Order is "a cancellable order"
      when  cancelOrder
      then  Order is "a cancelled order"
    }

    example "too late after shipping" {
      given Order is "a shipped order"
      when  cancelOrder
      then  error NotCancellable
    }
  }
}