lukego

sed -E -e 's/^/    /g' -e 's/^    --- ?//g' | pandoc -o listing.pdf -

That expression is a cheap literate programming system for Markdown.
Start commentary lines with '--- ' and they will be
markdown-formatted, the rest will be code. (Uses Lua comment syntax.)

Finally the right implementation of this idea:
  http://fresh.homeunix.net/~luke/misc/emacs/pbook.pdf (program)
  http://fresh.homeunix.net/~luke/misc/erlang/regtest.pdf (better example)