private static MoveCandidate GetMoveCandidate(this Board board, Position origin, Direction direction)
=> board[origin].Match(
number => new MoveCandidate(number, origin, board.FindMoveTarget(origin, direction)),
() => new MoveCandidate(0, origin, Maybe <Position> .Nothing)
);
public static Maybe <Position> FindMoveTarget(this Board board, Position position, Direction direction)
=> board[position].Match(
number => board.FindMoveTarget(number, board.BuildPositionPairs(position, direction).ToArray()),
() => Maybe <Position> .Nothing
);
