Hi Beginners. I'm trying to write a matrix class, for a game of life implementation, and am having trouble with the vicinityMatrix function. When I define it inside the class I get the error "Could not deduce (Matrix m (Maybe a)) from the context (Matrix m a)". However when I define it inside ghci, there is no problem: :t \m x y -> fromRows $ vicinityRows m x y \m x y -> fromRows $ vicinityRows m x y :: forall (m :: * -> *) (m1 :: * -> *) a. (Matrix m (Maybe a), Matrix m1 a) => m1 a -> Integer -> Integer -> m (Maybe a) How would I modify my class to allow the definition? The class is defined below. module Matrix (Matrix) where import Data.Array import Data.Maybe (catMaybes) import Control.Monad (guard) class Matrix m a where fromRows :: [[a]] -> m a toList :: m a -> [a] rows :: m a -> Integer columns :: m a -> Integer row :: m a -> Integer -> [a] column :: m a -> Integer -> [a] at :: m a -> Integer -> Integer -> a (!!!) :: m a -> Integer -> Integer -> a vicinityRows :: m a -> Integer -> Integer -> [[Maybe a]] vicinityMatrix :: m a -> Integer -> Integer -> m (Maybe a) neighbours :: m a -> Integer -> Integer -> [a] toList m = do x <- [0 .. columns m - 1] y <- [0 .. rows m - 1] return $ at m x y row m n = [at m x n | x <- [0 .. columns m - 1]] column m n = [at m n y | y <- [0 .. rows m - 1]] at = (!!!) (!!!) = at vicinityRows m x y = do x' <- [x - 1 .. x + 1] return $ do y' <- [y - 1 .. y + 1] return cell where cell | x < 0 = Nothing | y < 0 = Nothing | x >= columns m = Nothing | y >= rows m = Nothing | otherwise = Just $ at m x y vicinityMatrix m x y = fromRows $ vicinityRows m x y