-- |
-- Filter 'Position's only leaving those which have a 'Snorkel' in some board.
areSnorkels :: Board -> Set.Set Position -> Set.Set Position
areSnorkels board = Set.filter (maybe False isSnorkel . getPiece board) . arePieces board
areSnorkels :: Board -> Set.Set Position -> Set.Set Position
areSnorkels board = Set.filter (maybe False isSnorkel . getPiece board) . arePieces board
areSnorkels board = Set.filter (maybe False isSnorkel . getPiece board) . arePieces board