Matrix multiplication threesome

matrix_mult.hs

dot :: [Int] -> [Int] -> Int
dot r1 r2 = sum (zipWith (*) r1 r2)

n_chunks :: Int -> [Int] -> Matrix
n_chunks _ [] = []
n_chunks n xs = take n xs: n_chunks n (drop n xs) 


timesM :: Matrix -> Matrix -> Matrix
timesM a b | not (valid a) || not (valid b) = error "Po hube dostanes!"
           | otherwise = n_chunks (length a) [ra `dot` cb | ra <- a, cb <- (transpose b) ]

-- Rosetta code:
mmult :: Num a => [[a]] -> [[a]] -> [[a]] 
mmult a b = [
    [ 
        sum (zipWith (*) ar bc) | bc <- (transpose b)
    ] 
        | ar <- a 
    ]


-- Curry
timesMap :: Matrix -> Matrix -> Matrix
timesMap _ [] = []
timesMap [] _ = []
timesMap a b = [map (dot ra) tb | ra <- a]
    where tb = transpose b