Scala exercise with types and abstraction

Write an API for playing tic-tac-toe. There should be no side-effects (or variables), at all, for real. The move function will take a game state, a Position and it will return a data type that you write yourself.

The following functions (at least) must be supported:

1. move (as mentioned)

2. whoseTurn (returns which player’s turn it is)

3. whoWon (returns who won or if a draw)

4. playerAt (returns which player, if any, is at a given position)

Importantly, the following must be true:

1. It is a compile-time error to call move or whoseTurn on a game that has been completed

2. It is a compile-time error to call whoWon on a game that has not been completed

3. The playerAt function must be supported on both complete and in-play games

Good luck and may the types be with you.