Multiplication tables: Difference between revisions

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@@ Line 2,254: / Line 2,254: @@
 Or, making do without imports beyond the Prelude, and separating data from formatting:
-<lang Haskell>multTable :: Int -> [[[Int]]]
+<lang Haskell>multTable :: Int -> [[Maybe Int]]
-multTable n = (\x -> [x]      :    [] : (
+multTable n =
-              (\y -> if y < x then [] else [x * y])
+    (\x ->   Just x    : Nothing : (
-                 <$> range))
+    (\y -> if y < x then Nothing else Just (x * y))
-                 <$> range
+        <$> range))
-              where  range = [1..n]
+        <$> range
+      where range = [1..n]
-tableString :: [[[Int]]] -> String
+tableString :: [[Maybe Int]] -> String
-tableString tbl = unlines $ (concat . (fmt <$>)) <$> tbl
+tableString tbl =
+    unlines $ (concat . (fmt <$>)) <$> tbl
-  where
-    pad     = "    "
-    fmt [ ] = pad
-    fmt [e] = drop (length s) (pad ++ s)
       where
-          s = show e
+        pad          = "    "
+        fmt  Nothing = pad
+        fmt (Just n) = drop (length s) (pad ++ s)
+          where
+            s = show n
 main :: IO ()