VIM-Metaprogramming is a project mainly written in Vim Script, it's free.
Metaprogramming in VIM scripts
This is a mirror of http://www.vim.org/scripts/script.php?script_id=3785
VIM scripts can edit themselves, thus we could 'edit', '?', 's', 'source' scripts to create some domain specific language like :
silent! 0,$s/\vFunc[(.+)]{(.+)}/fun!\1\r\2\rendfun\r/g Func[Test()]{return 3}
Notice the function is considered one-liner. I hope it is helpful.