grid.hs

import qualified Line
import Data.Maybe

newtype Grid a = Grid { grid :: Line.Line (Line.Line a) } deriving Show

instance Functor Grid where 
	fmap f = Grid . (fmap . fmap) f . grid

extract :: Grid a -> a
extract = Line.extract . Line.extract . grid

left :: Grid a -> Maybe (Grid a)
left = fmap Grid . Line.left . grid

right :: Grid a -> Maybe (Grid a)
right = fmap Grid . Line.right . grid

up :: Grid a -> Maybe (Grid a)
up = fmap Grid . pull_maybe . fmap Line.left . grid

down :: Grid a -> Maybe (Grid a)
down = fmap Grid . pull_maybe . fmap Line.right . grid

pull_maybe :: Line.Line (Maybe a) -> Maybe (Line.Line a)
pull_maybe (Line.Line ls x rs) = check (distribute ls) x (distribute rs) where
	check (Just _ls) (Just _x) (Just _rs) = Just $ Line.Line _ls _x _rs
	check _ _ _ = Nothing

distribute :: [Maybe a] -> Maybe [a]
distribute [] = pure []
distribute (ax:axs) = (:) <$> ax <*> (distribute axs)