Add Haskell solutions for Problems 1, 2, 3

Haskell/p003.hs

@@ -0,0 +1,23 @@
+-- The prime factors of 13195 are 5, 7, 13 and 29.  --
+-- What is the largest prime factor of the number 600851475143?
+
+isPrime :: (Integral n) => n -> Bool
+isPrime 1 = False
+isPrime 2 = True
+isPrime 3 = True
+isPrime n =
+    n `mod` 2 /= 0 && n `mod` 3 /= 0 && null [ x | x <- candidates, n `mod` x == 0 || n `mod` (x+2) == 0 ]
+    where candidates = [5,11..limit]
+          limit = floor(sqrt(fromIntegral n)) + 1
+
+maxPrimeFactor :: (Integral n) => n -> n
+maxPrimeFactor n
+    | isPrime n         = n         
+    | n `mod` 2 == 0    = maxPrimeFactor $ fromIntegral n `div` 2
+    | otherwise         = maxPrimeFactor $ fromIntegral n `div` head [i | i <- [3,5..], n `mod` i == 0 && isPrime i]
+
+main :: IO ()
+main = do
+    let result = maxPrimeFactor 600851475143
+    putStrLn $ "Project Euler, Problem 3\n"
+        ++ "Answer: " ++ (show result)