improve sorting

make-pages/GalleryPage.hs

@@ -1,10 +1,12 @@
+{-# LANGUAGE TransformListComp #-}
 module GalleryPage (make) where
 
 import Control.Exception
-import Data.Function (on, (&))
-import Data.List (sortBy, groupBy)
+import Data.Function (on)
+import Data.List (sortOn, groupBy)
 import qualified Data.Text.Lazy as Lazy
 import System.FilePath ((</>), takeDirectory)
+import GHC.Exts (Down (..), the)
 
 import BuilderQQ
 import Depend (thumbFile)
@@ -42,12 +44,12 @@ make' title nsfw infos = [b|@0
  where
   items = map (uncurry $ makeYearItems nsfw) infosByYear
   infosByYear =
-    infos & sortBy  (cmpInfo `on` #second)
-          & map     (\fi -> (fi, #year $ #second fi))
-          & groupBy ((==) `on` #second)
-          & map     (\ys -> (#second (head ys), map #first ys))
-  cmpInfo (Info {date = d1, title = t1}) (Info {date = d2, title = t2}) =
-    compare d2 d1 <> compare t1 t2
+    [(the year, infopath) |
+      infopath@(_, info) <- infos,
+      then sortOn by Down info,
+      let year = #year info,
+      then group by Down year using groupBy']
+  groupBy' f = groupBy ((==) `on` f)
 
 makeYearItems :: Bool -- ^ nsfw
               -> Integer -- ^ year