Bollocks – I can’t work out how to pass the co-ordinates of the afflicted grid-square to the appropriate exception. So instead, the afflicted grid-square calls the exception, which then creates a message such as ‘there are too many ogres in a grid square’. Control then goes back to the code for the grid-square, which augments the message with ‘The afflicted grid-square has co-ordinates (x, y).’ and then displays the complete message.

It works but it’s not satisfactory to me.