2016 Update

Task/Fibonacci-sequence/Haskell/fibonacci-sequence-4.hs

@@ -1,15 +1,2 @@
-import Data.List
-
-xs <+> ys = zipWith (+) xs ys
-xs <*> ys = sum $ zipWith (*) xs ys
-
-newtype Mat a = Mat {unMat :: [[a]]} deriving Eq
-
-instance Show a => Show (Mat a) where
-  show xm = "Mat " ++ show (unMat xm)
-
-instance Num a => Num (Mat a) where
-  negate xm = Mat $ map (map negate) $ unMat xm
-  xm + ym   = Mat $ zipWith (<+>) (unMat xm) (unMat ym)
-  xm * ym   = Mat [[xs <*> ys | ys <- transpose $ unMat ym] | xs <- unMat xm]
-  fromInteger n = Mat [[fromInteger n]]
+fib :: Integer -> Integer
+fib n = fst $ foldl (\(a, b) _ -> (b, a + b)) (0, 1) [1 .. n]