Solve 'Convert to Binary' kata

Author: borisskert

src/Binary.hs

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+module Binary (toBinary) where
+
+-- https://www.codewars.com/kata/59fca81a5712f9fa4700159a/train/haskell
+
+toBinary :: Integer -> Integer
+toBinary = bitsToBinary . integerToBits
+
+integerToBits :: Integer -> [Bool]
+integerToBits 0 = []
+integerToBits x
+  | even x = False : integerToBits (x `div` 2)
+  | otherwise = True : integerToBits (x `div` 2)
+
+bitsToBinary :: [Bool] -> Integer
+bitsToBinary [] = 0
+bitsToBinary (False : xs) = (* 10) . bitsToBinary $ xs
+bitsToBinary (True : xs) = (+ 1) . (* 10) . bitsToBinary $ xs
+
+-- #againwhatlearned: Use `showBin` of the `Numeric` module
+-- import Numeric (showBin)
+-- toBinary :: Integer -> Integer
+-- toBinary = read . flip showBin ""

test/BinarySpec.hs

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+module BinarySpec where
+
+import Binary (toBinary)
+import Test.Hspec
+
+spec :: Spec
+spec = do
+  describe "Fixed Tests" $ do
+    it "toBinary 1" $ toBinary 1 `shouldBe` 1
+    it "toBinary 2" $ toBinary 2 `shouldBe` 10
+    it "toBinary 3" $ toBinary 3 `shouldBe` 11
+    it "toBinary 5" $ toBinary 5 `shouldBe` 101