stop relying on undefined in RenderCell

posts/number-number/2/Diagonal.hs

@@ -14,25 +14,27 @@ instance Show RowNumber where
 
 -- Rendered cell data, along with its row number and an optional value to show instead
 data RenderCell a = RC {
-    cellRow :: Maybe RowNumber,
+    cellRow :: Maybe RowNumber,  -- Nothing if this is a header; Just . RC otherwise
-    cellForceShow :: Maybe String,
+    cellForceShow :: Maybe String,  -- TODO: Either String a
-    cellData :: a
+    cellData :: Maybe a
   } deriving Functor
 
 -- If a forced value is availaible, use it; otherwise, show the inside
 instance Show a => Show (RenderCell a) where
-  show (RC _ Nothing x)  = show x
+  show (RC _ Nothing (Just x)) = show x
-  show (RC _ (Just s) _) = s
+  show (RC _ Nothing Nothing)  = ""
+  show (RC _ (Just s) _)       = s
 
 -- Lift a RenderCell over Either to an Either over RenderCells
--- If the force-string is set, then a `Left` version with an undefined value is returned
+-- If the force-string is set, then a `Left` version with a Nothing value is returned
 liftRC :: RenderCell (Either a b) -> Either (RenderCell a) (RenderCell b)
-liftRC (RC rn (Just x) _) = Left $ RC rn (Just x) undefined
+liftRC (RC rn Nothing Nothing) = Left $ RC rn Nothing Nothing
-liftRC (RC rn Nothing (Left v)) = Left $ RC rn Nothing v
+liftRC (RC rn (Just x) _) = Left $ RC rn (Just x) Nothing
-liftRC (RC rn Nothing (Right v)) = Right $ RC rn Nothing v
+liftRC (RC rn Nothing (Just (Left v))) = Left $ RC rn Nothing $ Just v
+liftRC (RC rn Nothing (Just (Right v))) = Right $ RC rn Nothing $ Just v
 
 -- Single column with a fixed header and data coming from a row number
-newColumn header f = columns f (\_ -> Headed $ RC Nothing (Just header) undefined) [()]
+newColumn header f = columns f (\_ -> Headed $ RC Nothing (Just header) Nothing) [()]
 
 -- Numbered rows of data, as opposed to data for rendering
 data DiagRow a = DR {
@@ -42,7 +44,7 @@ data DiagRow a = DR {
 
 -- Same as `newColumn`, but reads into a DiagRow's row numberRows
 -- The display function `f` is used to convert the value to a String
-newColumnR header f = newColumn header (\_ c -> RC (Just $ rowNumber c) (Just $ f $ rowNumber c) undefined)
+newColumnR header f = newColumn header (\_ c -> RC (Just $ rowNumber c) (Just $ f $ rowNumber c) Nothing)
 
 -- Number rows with the title "Sequence"
 numberColumn = newColumnR "Sequence" show
@@ -53,9 +55,9 @@ ellipsisColumn = newColumnR "..." (const "...")
 -- The ellipsis row is mapped to a cells which always display as ellipses
 -- The remaining rows are `Right` if they lie on the main diagonal, or `Left` otherwise
 diagBox' n = columns cell headCell [0..n]
-  where cell _ (DR Ellipsis  _) = RC (Just Ellipsis) (Just "...") undefined
+  where cell _ (DR Ellipsis  _) = RC (Just Ellipsis) (Just "...") Nothing
-        cell i (DR rn       rd) = RC (Just rn) Nothing $ (if RN i == rn then Right else Left) (rd !! i)
+        cell i (DR rn       rd) = RC (Just rn) Nothing $ Just $ (if RN i == rn then Right else Left) (rd !! i)
-        headCell i = Headed $ RC Nothing (Just $ show i) undefined
+        headCell i = Headed $ RC Nothing (Just $ show i) Nothing
 
 diagBox n = numberColumn <> diagBox' n <> ellipsisColumn
 
@@ -71,6 +73,15 @@ displayRows f = (displayTable .) . tagRows'
 rowsOmega :: [[a]] -> [a] -> [DiagRow a]
 rowsOmega xs y = zipWith (\x n -> DR (RN n) x) xs [0..] ++ [DR Ellipsis [], DR Omega y]
 
+diagData = rowsOmega [
+    [1, 2, 3, 4, 5, 6],
+    [9, 2, 4, 8, 3, 7],
+    [2, 2, 8, 2, 2, 2],
+    [2, 3, 9, 3, 9, 9],
+    [9, 4, 9, 4, 9, 4],
+    [8, 1, 2, 5, 7, 9]
+  ]
+  [2, 3, 9, 4, 0, 0]
 
 displayDiagTable ps = rmap style . diagBox
   where style    = either show id . displayRows (("Red " ++) . show) (map (, ("Green " ++). show) ps)