# Pastebin jOzAUQdg
navLink :: [String] -> Item String -> Compiler String
navLink args item =
  return $ "<a " ++ classAttr ++ "href='" ++ to ++ "'>" ++ title ++ "</a>"
 where
  [to, title] = args
  itemName    = show $ itemIdentifier item
  classAttr   = if (navLinkIsActive to itemName) then " class='active' " else ""

navLinkIsActive :: String -> String -> Bool
navLinkIsActive to itemName
  | to == "/" && itemName == "index.html"
  = True
  | Just m <- matchPattern "^([^/.]+)\\.html$"
  = to == "/" ++ m ++ ".html"
  | Just _ <- matchPattern "^posts/([^/.]+)\\.md$"
  = to == "/blog.html"
  | Just _ <- matchPattern "^info/([^/.]+)\\.md$"
  = to == "/info.html"
  | Just m <- matchPattern "^([^/.]+)\\.md$"
  = to == "/" ++ m ++ ".md"
  | Just m <- matchPattern "^templates/([^.]+)\\.md$"
  = to == "/" ++ m ++ ".html"
  | otherwise
  = error (to ++ " / " ++ itemName)
 where
  firstMatch :: (String, String, String, [String]) -> Maybe String
  firstMatch (_, _, _, [name]) = Just name
  firstMatch _                 = Nothing
  matchPattern :: String -> Maybe String
  matchPattern pat = firstMatch $ itemName =~ pat