diamond: Change return type to Maybe

exercises/diamond/examples/success-standard/src/Diamond.hs

@@ -9,8 +9,8 @@ oneRow :: Char -> (Int, Int) -> String
 oneRow c (0, y) = pad y ++ [c] ++ pad y
 oneRow c (x, y) = pad y ++ [c] ++ pad x ++ [c] ++ pad y
 
-diamond :: Char -> [String]
-diamond = (\x -> x ++ tail (reverse x)) . mkTop . subtract 64 . ord
+diamond :: Char -> Maybe [String]
+diamond = Just . (\x -> x ++ tail (reverse x)) . mkTop . subtract 64 . ord
   where rows x = zip (0 : take (x-1) [1, 3..]) [x-1, x-2..0]
         mkTop  = zipWith oneRow abc . rows
         abc    = map chr [65..90]

exercises/diamond/package.yaml

@@ -1,5 +1,5 @@
 name: diamond
-version: 1.1.0.2
+version: 1.1.0.3
 
 dependencies:
   - base

exercises/diamond/src/Diamond.hs

@@ -1,4 +1,4 @@
 module Diamond (diamond) where
 
-diamond :: Char -> [String]
+diamond :: Char -> Maybe [String]
 diamond = error "You need to implement this function"

exercises/diamond/test/Tests.hs

@@ -14,7 +14,7 @@ specs = describe "diamond" $ for_ cases test
 
     test Case{..} = it description assertion
       where
-        assertion = diamond input `shouldBe` expected
+        assertion = diamond input `shouldBe` Just expected
 
 
 data Case = Case { description :: String