Long primes: Difference between revisions

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 </pre>
 =={{header|Haskell}}==
-<lang Haskell>
+<lang Haskell>import Data.List (elemIndex)
-import Data.List
 longPrimesUpTo :: Int -> [Int]
-longPrimesUpTo n = filter isLongPrime $ takeWhile (<n) primes
+longPrimesUpTo n =
+  filter isLongPrime $
-  where sieve (p:xs) = p : sieve [x | x <- xs, x `mod` p /= 0]
-        primes = sieve [2..]
+    takeWhile (< n) primes
+  where
-        isLongPrime n = found
-          where cycles = take n (iterate (\y -> 10 * y `mod` n) 1)
+    sieve (p : xs) = p : sieve [x | x <- xs, x `mod` p /= 0]
+    primes = sieve [2 ..]
-                index = findIndex (== head cycles) $ tail cycles
+    isLongPrime n = found
-                found = case index of (Just i) -> n - i == 2
+      where
-                                      _        -> False
+        cycles = take n (iterate ((`mod` n) . (10 *)) 1)
+        index = elemIndex (head cycles) $ tail cycles
+        found = case index of
+          (Just i) -> n - i == 2
+          _ -> False
 display :: Int -> IO ()
-display n = if n <= 64000 then do
+display n =
+  if n <= 64000
-              putStrLn (show n ++ " is " ++ show (length $ longPrimesUpTo n))
+    then do
-              display (n * 2)
-            else pure ()
+      putStrLn
+        ( show n <> " is "
+            <> show (length $ longPrimesUpTo n)
+        )
+      display (n * 2)
+    else pure ()
 main :: IO ()
 main = do
   let fiveHundred = longPrimesUpTo 500
+  putStrLn
-  putStrLn ("The long primes up to 35 are:\n" ++ show fiveHundred ++ "\n")
+    ( "The long primes up to 35 are:\n"
-  putStrLn ("500 is " ++ show (length fiveHundred))
+        <> show fiveHundred
-  display 1000
+        <> "\n"
-</lang>
+    )
+  putStrLn ("500 is " <> show (length fiveHundred))
+  display 1000</lang>
 {{out}}
+<pre>The long primes up to 35 are:
-<pre>
-The long primes up to 35 are:
 [7,17,19,23,29,47,59,61,97,109,113,131,149,167,179,181,193,223,229,233,257,263,269,313,337,367,379,383,389,419,433,461,487,491,499]
@@ Line 870: / Line 881: @@
 is 716
 is 1300
-is 2430
+is 2430</pre>
-</pre>
 =={{header|J}}==