main-loop-psuedo.txt

# gameBoard represents the current, valid state of the game
# including which pieces are on which squares
gameBoard = null

# who's turn is it to move?
turn = unknown

while true:
	# read board will return an incomplete gameBoard object, consisting of
	# the colors of pieces on their respective squares, but not the pieces.
	# We'll determine what the pieces are based on the diff between the scan
	# and gameBoard.
	scanBoard = readBoard()

	if isStartingPosition(scanBoard):
		# this is a new game
		gameBoard = startingBoard()
		turn = white
	else:
		# validate the move

		if gameBoard == null or turn == unknown:
			showWaitingForGameToStart()
			continue
		
		changes = diffBoard(gameBoard, scanBoard)
				
		if len(changes) = 0:
			continue
	
		if len(changes) == 1 or len(changes) > 4:
			# we can't distinguish what move(s) happened.
			showError()
			continue
	
		if len(changes) == 3 and !isEnPassant(gameBoard, changes, turn):
			showError()
			continue
			
		if len(changes) == 4 and !isCastle(gameBoard, changes, turn):
			showError()
			continue()	
		
		if colorOfMove(gameBoard, changes, turn) != turn:
			showError()
			continue
	
		# at this point, we know that either there's a castle or
		# two squares have changed, resulting in a piece of turn's color
		# moving and optionally capturing a piece of turn's opponent.
		# This is a valid turn for our purposes, we won't verify
		# the move is legal -- commit the board
		gameBoard = commitMove(gameBoard, changes)
	
	if findComputerColor() == turn:
		computeAndDisplayMove(gameBoard)

	if turn == white:
		turn = black
	else
		turn = white