YAPC::EU 2018 Glasgow Update!

Task/Parallel-calculations/Haskell/parallel-calculations-1.hs

@@ -1,30 +1,47 @@
-import Control.Parallel.Strategies
-import Control.DeepSeq
-import Data.List
-import Data.Function
+import Control.Parallel.Strategies (parMap, rdeepseq)
+import Control.DeepSeq (NFData)
+import Data.List (maximumBy)
+import Data.Function (on)
 
 nums :: [Integer]
-nums = [112272537195293
-       ,112582718962171
-       ,112272537095293
-       ,115280098190773
-       ,115797840077099
-       ,1099726829285419]
+nums =
+  [ 112272537195293
+  , 112582718962171
+  , 112272537095293
+  , 115280098190773
+  , 115797840077099
+  , 1099726829285419
+  ]
 
-lowestFactor :: Integral a => a -> a -> a
-lowestFactor s n | n `rem` 2 == 0 = 2
-                 | otherwise      = head $ y
-  where y = [x | x <- [s..ceiling . sqrt $ fromIntegral n]
-            ++ [n], n `rem` x == 0, x `rem` 2 /= 0]
+lowestFactor
+  :: Integral a
+  => a -> a -> a
+lowestFactor s n
+  | even n = 2
+  | otherwise = head y
+  where
+    y =
+      [ x
+      | x <- [s .. ceiling . sqrt $ fromIntegral n] ++ [n]
+      , n `rem` x == 0
+      , odd x ]
 
+primeFactors
+  :: Integral a
+  => a -> a -> [a]
 primeFactors l n = f n l []
-    where f n l xs = if n > 1 then f (n `div` l) (lowestFactor (max l 3)  (n `div` l)) (l:xs)
-                              else xs
+  where
+    f n l xs =
+      if n > 1
+        then f (n `div` l) (lowestFactor (max l 3) (n `div` l)) (l : xs)
+        else xs
 
-minPrimes ns = (\(x,y) -> (x,primeFactors y x)) $
-              maximumBy (compare `on` snd) $
-              zip ns (parMap rdeepseq (lowestFactor 3) ns)
+minPrimes
+  :: (Control.DeepSeq.NFData a, Integral a)
+  => [a] -> (a, [a])
+minPrimes ns =
+  (\(x, y) -> (x, primeFactors y x)) $
+  maximumBy (compare `on` snd) $ zip ns (parMap rdeepseq (lowestFactor 3) ns)
 
 main :: IO ()
-main = do
-    print $ minPrimes nums
+main = print $ minPrimes nums