Hakyll, list posts grouped by year

gistfile1.hs

---- group posts by years

groupByYear :: [Page a] -> [(String, [Page a])]
groupByYear = map (\pg -> ( year (head pg), pg) ) .
              groupBy (\ a b -> year a == year b)
  where year :: Page a -> String
        year = take 4 . takeBaseName . getField "path"


addYearList :: String
            -> [Page String]
            -> Compiler () (Page String)
addYearList y posts = constA (mempty, posts)
                      >>> addPostList
                      >>> arr (setField "postsYear" y)
                      >>> applyTemplateCompiler "templates/postsYear.html"