Protect partial uses of maximum with NonEmpty.

2 files changed, 23 insertions, 24 deletions

diff --git a/src/Text/Pandoc/Writers/Powerpoint/Output.hs b/src/Text/Pandoc/Writers/Powerpoint/Output.hs
index 4dbf32c4e..0e515b3c2 100644
--- a/src/Text/Pandoc/Writers/Powerpoint/Output.hs
+++ b/src/Text/Pandoc/Writers/Powerpoint/Output.hs
@@ -475,15 +475,16 @@ registerLink link = do
   linkReg <- gets stLinkIds
   mediaReg <- gets stMediaIds
   hasSpeakerNotes <- curSlideHasSpeakerNotes
-  let maxLinkId = case M.lookup curSlideId linkReg of
-        Just mp -> case M.keys mp of
-          [] -> if hasSpeakerNotes then 2 else 1
-          ks -> maximum ks
-        Nothing -> if hasSpeakerNotes then 2 else 1
-      maxMediaId = case M.lookup curSlideId mediaReg of
-        Just [] -> if hasSpeakerNotes then 2 else 1
-        Just mInfos -> maximum $ map mInfoLocalId mInfos
-        Nothing -> if hasSpeakerNotes then 2 else 1
+  let maxLinkId = case M.lookup curSlideId linkReg >>= nonEmpty . M.keys of
+        Just xs -> maximum xs
+        Nothing
+          | hasSpeakerNotes -> 2
+          | otherwise       -> 1
+      maxMediaId = case M.lookup curSlideId mediaReg >>= nonEmpty of
+        Just mInfos -> maximum $ fmap mInfoLocalId mInfos
+        Nothing
+          | hasSpeakerNotes -> 2
+          | otherwise       -> 1
       maxId = max maxLinkId maxMediaId
       slideLinks = case M.lookup curSlideId linkReg of
         Just mp -> M.insert (maxId + 1) link mp
@@ -498,20 +499,19 @@ registerMedia fp caption = do
   mediaReg <- gets stMediaIds
   globalIds <- gets stMediaGlobalIds
   hasSpeakerNotes <- curSlideHasSpeakerNotes
-  let maxLinkId = case M.lookup curSlideId linkReg of
-        Just mp -> case M.keys mp of
-          [] -> if hasSpeakerNotes then 2 else 1
-          ks -> maximum ks
-        Nothing -> if hasSpeakerNotes then 2 else 1
-      maxMediaId = case M.lookup curSlideId mediaReg of
-        Just [] -> if hasSpeakerNotes then 2 else 1
-        Just mInfos -> maximum $ map mInfoLocalId mInfos
-        Nothing -> if hasSpeakerNotes then 2 else 1
+  let maxLinkId = case M.lookup curSlideId linkReg >>= nonEmpty . M.keys of
+          Just ks -> maximum ks
+          Nothing
+            | hasSpeakerNotes -> 2
+            | otherwise       -> 1
+      maxMediaId = case M.lookup curSlideId mediaReg >>= nonEmpty of
+          Just mInfos -> maximum $ fmap mInfoLocalId mInfos
+          Nothing
+            | hasSpeakerNotes -> 2
+            | otherwise       -> 1
       maxLocalId = max maxLinkId maxMediaId
 
-      maxGlobalId = case M.elems globalIds of
-        [] -> 0
-        ids -> maximum ids
+      maxGlobalId = maybe 0 maximum $ nonEmpty $ M.elems globalIds
 
   (imgBytes, mbMt) <- P.fetchItem $ T.pack fp
   let imgExt = (mbMt >>= extensionFromMimeType >>= (\x -> return $ "." <> x))
diff --git a/src/Text/Pandoc/Writers/Powerpoint/Presentation.hs b/src/Text/Pandoc/Writers/Powerpoint/Presentation.hs
index affec38aa..9246a93e9 100644
--- a/src/Text/Pandoc/Writers/Powerpoint/Presentation.hs
+++ b/src/Text/Pandoc/Writers/Powerpoint/Presentation.hs
@@ -45,6 +45,7 @@ module Text.Pandoc.Writers.Powerpoint.Presentation ( documentToPresentation
 import Control.Monad.Reader
 import Control.Monad.State
 import Data.List (intercalate)
+import Data.List.NonEmpty (nonEmpty)
 import Data.Default
 import Text.Pandoc.Definition
 import Text.Pandoc.ImageSize
@@ -363,9 +364,7 @@ inlineToParElems (Note blks) = do
     then return []
     else do
     notes <- gets stNoteIds
-    let maxNoteId = case M.keys notes of
-          [] -> 0
-          lst -> maximum lst
+    let maxNoteId = maybe 0 maximum $ nonEmpty $ M.keys notes
         curNoteId = maxNoteId + 1
     modify $ \st -> st { stNoteIds = M.insert curNoteId blks notes }
     local (\env -> env{envRunProps = (envRunProps env){rLink = Just $ InternalTarget endNotesSlideId}}) $