Long multiplication: Difference between revisions

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@@ Line 2,359: / Line 2,359: @@
 import Data.Char (digitToInt)
-digits :: Integer -> [Integer]
+longmult :: Integer -> Integer -> Integer
+longmult x y = foldl1 ((+) . (10 *)) (polymul (digits x) (digits y))
-digits = fmap (fromIntegral . digitToInt) . show
-lZZ :: [[Integer]]
-lZZ = inits $ repeat 0
-table :: (Integer -> Integer -> Integer) -> [Integer] -> [Integer] -> [[Integer]]
-table f x = fmap $ flip fmap x . f
 polymul :: [Integer] -> [Integer] -> [Integer]
-polymul xs ys = fmap sum (transpose (zipWith (++) lZZ (table (*) xs ys)))
+polymul xs ys =
+  sum <$>
+  transpose
+    (zipWith
+       (++)
+       (inits $ repeat 0)
+       ((\f x -> fmap $ flip fmap x . f) (*) xs ys))
-longmult :: Integer -> Integer -> Integer
+digits :: Integer -> [Integer]
+digits = fmap (fromIntegral . digitToInt) . show
-longmult x y = foldl1 ((+) . (10 *)) (polymul (digits x) (digits y))
 main :: IO ()