Sudoku solver with Haskell.
Unfortunately, doing it in functional is hard. First, there is no pointer in Haskell.
Implementing a circular doubly-linked-list is possible through tying the knot. But creating a torus data structure, where the up, down, left and right of a node is circular is hard. Implementing the Dancing Links cover and uncover method is hard for me at the moment, and hence I leave the repo as it is until I discover more about Haskell, and a more functional solution.