Solve 'Is it even?' kata

Author: borisskert

src/Even.hs

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+module Even (isEven) where
+
+-- https://www.codewars.com/kata/555a67db74814aa4ee0001b5/train/haskell
+
+isEven :: Double -> Bool
+isEven n = remainder == 0.0
+  where
+    (_, remainder) = divMod' n 2
+
+divMod' :: Double -> Int -> (Int, Double)
+divMod' a b = (d', a - d * b')
+  where
+    b' = fromIntegral b :: Double
+    d' = floor (a / b') :: Int
+    d = fromIntegral d' :: Double
+
+-- #againwhatlearned: Use mod' or divMod' from Data.Fixed module:
+-- import Data.Fixed (mod')
+-- isEven n = mod' n 2 == 0

test/EvenSpec.hs

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+module EvenSpec where
+
+import Even (isEven)
+import Test.Hspec
+import Text.Printf (printf)
+
+spec :: Spec
+spec = do
+  describe "Fixed Tests" $ do
+    it "isEven 0" $ isEven 0 `shouldBe` True
+    it "isEven 0.5" $ isEven 0.5 `shouldBe` False
+    it "isEven 1" $ isEven 1 `shouldBe` False
+    it "isEven 2" $ isEven 2 `shouldBe` True
+    it "isEven (-4)" $ isEven (-4) `shouldBe` True
+    it "isEven 15" $ isEven 15 `shouldBe` False
+    it "isEven 20" $ isEven 20 `shouldBe` True
+    it "isEven 220" $ isEven 220 `shouldBe` True
+    it "isEven 222222221" $ isEven 222222221 `shouldBe` False
+    it "isEven 500000000" $ isEven 500000000 `shouldBe` True