haskell: add [p4, p10]

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

haskell/p6.hs

@@ -0,0 +1,11 @@
+main :: IO ()
+main = putStr $ show $ solve 100
+
+solve :: Integer -> Integer
+solve n = squareOfSum n - sumOfSquares n
+  where
+    squareOfSum :: Integer -> Integer
+    squareOfSum n = sum [1 .. n] ^ 2
+
+    sumOfSquares :: Integer -> Integer
+    sumOfSquares n = sum $ map (^ 2) [1 .. n]