Pandoc filter to render frames around content

gistfile1.hs

{-# LANGUAGE OverloadedStrings #-}
module Main where

-- https://groups.google.com/d/msgid/pandoc-discuss/45a32eb9-23b9-4df1-8c6e-2e08073df166%40googlegroups.com?utm_medium=email&utm_source=footer

import Text.Pandoc.JSON
import Text.Pandoc.Definition
import Text.Printf
import Data.Maybe

main :: IO ()
main = toJSONFilter findFrame

defaultDisplayStyle :: String
defaultDisplayStyle = "frame"

defaultTitle :: String
defaultTitle = ""

findFrame :: Block -> Block
findFrame e@(Div as@(uid, classes, kvs) is)
  | "frame" `elem` classes =
    let displayStyle = fromMaybe defaultDisplayStyle (lookup "style" kvs)
        frameTitle   = fromMaybe defaultTitle (lookup "title" kvs) in
    Div as ([mkEnv displayStyle frameTitle] ++ is ++ [closeEnv])
  | otherwise = e
findFrame e = e

mkEnv :: String -> String -> Block
mkEnv st tit = RawBlock "latex" $ printf "\\begin{mdframed}[style={%s},frametitle={%s}]" st tit

closeEnv :: Block
closeEnv = RawBlock "latex" "\\end{mdframed}"