[Dev-luatex] Very simple sample?

Hello, I'm trying to use \directlua, but until now all may attempts failed. I begun with: \documentclass{book} \begin{document} \directlua0{tex.print("\uppercase{hello}");} \end{document} and then wrapped \directlua with every combination possible of \texscantokens, \luaescapestring, \scantokens and so on, but nothing seems to work (no errors, but I get "uppercase" printed, perhaps with dashes and quotes, and of course "hello" still in lower case). Please, could you provide an example showing what I should do. Are \directlua and tex.print the right commands to use? Thanks Javier