Family Day update

Task/Matrix-multiplication/Haskell/matrix-multiplication-3.hs

@@ -1,26 +1,10 @@
-foldlZipWith::(a -> b -> c) -> (d -> c -> d) -> d -> [a] -> [b]  -> d
-foldlZipWith _ _ u [] _          = u
-foldlZipWith _ _ u _ []          = u
-foldlZipWith f g u (x:xs) (y:ys) = foldlZipWith f g (g u (f x y)) xs ys
+multiply :: Num a => [[a]] -> [[a]] -> [[a]]
+multiply us vs = map (mult [] vs) us
+  where
+    mult xs [] _ = xs
+    mult xs _ [] = xs
+    mult [] (zs:zss) (y:ys) = mult (map (y *) zs) zss ys
+    mult xs (zs:zss) (y:ys) = mult (zipWith (\u v -> u + v * y) xs zs) zss ys
 
-foldl1ZipWith::(a -> b -> c) -> (c -> c -> c) -> [a] -> [b] -> c
-foldl1ZipWith _ _ [] _          = error "First list is empty"
-foldl1ZipWith _ _ _ []          = error "Second list is empty"
-foldl1ZipWith f g (x:xs) (y:ys) = foldlZipWith f g (f x y) xs ys
-
-multAdd::(a -> b -> c) -> (c -> c -> c) -> [[a]] -> [[b]] -> [[c]]
-multAdd f g xs ys = map (\us -> foldl1ZipWith (\u vs -> map (f u) vs) (zipWith g) us ys) xs
-
-mult:: Num a => [[a]] -> [[a]] -> [[a]]
-mult xs ys = multAdd (*) (+) xs ys
-
-test a b = do
-  let c = mult a b
-  putStrLn "a ="
-  mapM_ print a
-  putStrLn "b ="
-  mapM_ print b
-  putStrLn "c = a * b = mult a b ="
-  mapM_ print c
-
-main = test [[1, 2],[3, 4]] [[-3, -8, 3],[-2,  1, 4]]
+main :: IO ()
+main = mapM_ print $ multiply [[1, 2], [3, 4]] [[-3, -8, 3], [-2, 1, 4]

Task/Matrix-multiplication/Haskell/matrix-multiplication-4.hs

@@ -0,0 +1,12 @@
+mult :: Num a => [[a]] -> [[a]] -> [[a]]
+mult uss vss =
+  map
+    ((\xs ->
+         if null xs
+           then []
+           else foldl1 (zipWith (+)) xs) .
+     zipWith (flip (map . (*))) vss)
+    uss
+
+main :: IO ()
+main = mapM_ print $ mult [[1, 2], [3, 4]] [[-3, -8, 3], [-2, 1, 4]]