-- we want to fold something like this
g = [
[ 1, 2, 3 ],
[ 4, 5, 6 ],
[ 7, 8, 9 ]
]
-- into a Cell { value=1, right=(the Cell with value 2), down=(the cell with value 4) }
data Cell a = Cell {
value :: a,
down :: Cell a,
right :: Cell a
}
| Nil
deriving Show
right' :: Cell a -> Cell a
right' c@(Cell {}) = right c
right' Nil = Nil
mkRow :: [a] -> Cell a -> Cell a
mkRow xs c = foldr mkCell Nil valAndDown
where valAndDown = zip xs (iterate right' c)
mkCell (v,d) r = Cell { value=v, down=d, right=r }
mkGrid :: [[a]] -> Cell a
mkGrid = foldr mkRow Nil
