Error handling

[elliotchance]

Still trying to work out what error handling will look like, here is a rough idea:

start:
    declare last-order-date is text

    # one line
    try to fetch last order date into last-order-date, on no-orders set last-order-date to "unknown", on missing-order display error-message, always display "Fetched order date"

    # one line with better spacing
    try to fetch last order date into last-order-date,
        on no-orders set last-order-date to "unknown",
        on missing-order display error-message,
        always display "Fetched order date"

    # multiline
    try
        fetch last order date into last-order-date
        display "Fetched order date"
    catch no-orders, set last-order-date to "unknown"
    catch missing-order do
        display error-message
    end

fetch last order date into dest (dest is text):
    raise error no-orders
    raise error missing-order with the message "Where did it go?"