]> Hi, > I didn't followed the thread closely, but did you have a look > at Ocsigen's way to implement params_type? Thanks for the suggestion. Actually, there's an Ocsigen connection with what I'm doing. The Node module we've been discussing is a simplification; the real problem is for a data type that can be converted into the XHTML.M data used in Ocsigen. (As was discussed some time ago in the Ocsigen mailing list, the XHTML.M module does not strictly enforce the nested link nodes rule of the W3C. Nevertheless I have been looking for a solution that does enforce this rule). Anyway, I took a brief look at the code you mentioned, and re-read the relevant section in the "Rapport Ocsigen" you wrote a while ago (when I first read that report I had no idea what GADTs were!). It does seem that we're all just cooking up workarounds to the lack of GADTs in Ocaml. Now, I recall Xavier Leroy mentioning this topic at the user meeting last year. It seems the theory is ready, but the compiler needs some work done before it can accommodate this new feature. Are there news on that front? Best regards, Dario Teixeira