Add Haskell solution for Problem 35

Haskell/p035.hs

@@ -0,0 +1,23 @@
+-- The number, 197, is called a circular prime because all rotations of the digits: 197, 971, and 719, are themselves prime.
+--
+-- There are thirteen such primes below 100: 2, 3, 5, 7, 11, 13, 17, 31, 37, 71, 73, 79, and 97.
+--
+-- How many circular primes are there below one million?
+
+import Data.List (inits, tails)
+import ProjectEuler (isPrime, primeSieve)
+
+isCircularPrime :: Int -> Bool
+isCircularPrime n
+    | n == 2                               = True
+    | any (`elem` ['0','2'..'8']) (show n) = False
+    | all (isPrime . read) rotations       = True
+    | otherwise                            = False
+    where rotations = zipWith (++) (tails (show n)) (init (inits (show n)))
+--isCircularPrime n = let rotations = zipWith (++) (tails (show n)) (init (inits (show n)))
+--                    in  all (isPrime . read) rotations
+
+main = do
+    let result = length $ filter isCircularPrime (takeWhile (<1000000) primeSieve)
+    putStrLn $ "Project Euler, Problem 35\n"
+        ++ "Answer: " ++ show result