Rezoom.SQL: Statically typed SQL for F#(github.com)

  // domain layer line item logic, includes business rules
  // returns the updated invoice
  let addLineItem invoiceId lineItem =
    plan {
      // query for the invoice
      let! invoice = DB.getInvoiceById invoiceId
      if invoice.IsSent then
        failwith "Can't edit this invoice because it has been sent"
      // run INSERT/UPDATE statement(s)
      do! DB.addInvoiceLineItem invoiceId lineItem
      // re-query for the invoice to get its current state
      return! DB.getInvoiceById invoiceId
    }