Playing the game

Playing is easy. The Mines datatype needs not to be explained right now, suffice it to say that it models the state of the playing field (including the mines, but also keeping track of which fields have been explored or flagged). To play with a set m of mines means to execute these steps over and over again:

• If the left mousebutton is released, call open with the button array, the mines and the position of the field we want to open (note clever -reduced notation). If open returns Nothing, we lose; otherwise, we play on with the new playing field.
• If the right mousebutton is released, call flag with the button array, the mines and the position. No evil may occur, just play on.
• If a mouse button is pressed (remember, even the middle button counts), the smiley should look worried. Normally any of the two release events above will occur within a short while so the smiley changes back, but if we press the middle button, the smiley stays worried. We consider this a feature, and in the best academic tradition leave it to the reader to come up with a solution.
• On the other, if a start event occurs, restart the game; this can happen e.g. if the users clicks the smiley in the middle of the game.

playOn takes care of the smiley when we (de)flagged or explored a field. It also checks wether we have won with the previous move; this is the case if there are no untouched fields left (i.e. all fields are either cleared or flagged). This works because we are only allowed to drop as many flags as there are mines on the field.