lots of langfilter stuff, mostly lántas script

langfilter/Lang.hs

@@ -0,0 +1,19 @@
+module Lang where
+
+import Text.Pandoc.Definition
+import Data.Char (toLower)
+import qualified Data.Text as Text
+import System.IO
+
+data Lang = Lántas deriving (Eq, Show)
+
+type Vars = (?lang :: Maybe Lang)
+
+toLang :: Maybe MetaValue -> IO (Maybe Lang)
+toLang (Just (MetaInlines [Str s])) = toLang (Just (MetaString s)) -- ugh
+toLang (Just (MetaString (Text.map toLower -> s)))
+  | s == "lántas" || s == "laantas" = pure $ Just Lántas
+toLang Nothing = pure Nothing
+toLang (Just ℓ) = do
+  hPutStrLn stderr $ "[WARN] unknown language: " <> show ℓ
+  pure Nothing