Solve 'Change two-dimensional array' kata

Author: borisskert

src/Matrix.hs

@@ -0,0 +1,18 @@
+module Matrix (matrix) where
+
+-- https://www.codewars.com/kata/581214d54624a8232100005f/train/haskell
+
+matrix :: [[Int]] -> [[Int]]
+matrix arr = changeDiags 0 arr
+
+changeDiags :: Int -> [[Int]] -> [[Int]]
+changeDiags _ [] = []
+changeDiags i (x : xs) = (changeRow i x :) . changeDiags (i + 1) $ xs
+
+changeRow :: Int -> [Int] -> [Int]
+changeRow index xs
+  | xs !! index < 0 = replace index 0 xs
+  | otherwise = replace index 1 xs
+
+replace :: Int -> a -> [a] -> [a]
+replace pos x xs = (take pos xs ++) . (x :) . drop (pos + 1) $ xs

test/MatrixSpec.hs

@@ -0,0 +1,66 @@
+module MatrixSpec where
+
+import Matrix (matrix)
+import Test.Hspec
+
+spec :: Spec
+spec = do
+  describe "Fixed Tests" $ do
+    mapM_
+      fixedTest
+      [ ( [ [-1, 4, -5, -9, 3],
+            [6, -4, -7, 4, -5],
+            [3, 5, 4, -9, -1],
+            [1, 5, -7, -8, -9],
+            [-3, 2, 1, -5, 6]
+          ],
+          [ [0, 4, -5, -9, 3],
+            [6, 0, -7, 4, -5],
+            [3, 5, 1, -9, -1],
+            [1, 5, -7, 0, -9],
+            [-3, 2, 1, -5, 1]
+          ]
+        ),
+        ( [ [-1, 4, -5, -9, 3],
+            [6, 8, -7, 4, -5],
+            [3, 5, 1, -9, -1],
+            [1, 5, -7, 15, -9],
+            [-3, 2, 1, -5, -6]
+          ],
+          [ [0, 4, -5, -9, 3],
+            [6, 1, -7, 4, -5],
+            [3, 5, 1, -9, -1],
+            [1, 5, -7, 1, -9],
+            [-3, 2, 1, -5, 0]
+          ]
+        ),
+        ( [ [-1, 4, -5, -9, 3, 8],
+            [6, 8, -7, 4, -5, -1],
+            [3, 5, 1, -9, -1, 6],
+            [1, 5, -7, 15, -9, 3],
+            [-3, 2, 1, -5, -6, 0],
+            [8, 2, 0, -2, 4, -5]
+          ],
+          [ [0, 4, -5, -9, 3, 8],
+            [6, 1, -7, 4, -5, -1],
+            [3, 5, 1, -9, -1, 6],
+            [1, 5, -7, 1, -9, 3],
+            [-3, 2, 1, -5, 0, 0],
+            [8, 2, 0, -2, 4, 0]
+          ]
+        ),
+        ( [ [1, 1, -5, 5],
+            [2, -4, 11, 2],
+            [3, 1, -1, 4],
+            [2, -6, 8, 10]
+          ],
+          [ [1, 1, -5, 5],
+            [2, 0, 11, 2],
+            [3, 1, 0, 4],
+            [2, -6, 8, 1]
+          ]
+        )
+      ]
+
+fixedTest :: ([[Int]], [[Int]]) -> SpecWith ()
+fixedTest (inp, ans) = it ("matrix " ++ show inp) $ matrix inp `shouldBe` ans