> That friend kept asking me to write a converter that would convert a file of TeX to a file of HTML. I kept telling him that such a converter was impossible because TeX was a programming language and HTML was not.

According to Massimiliano Gubinelli (please take a look at the following comments thread https://news.ycombinator.com/item?id=27820466, in particular at https://news.ycombinator.com/item?id=27822662), the reason why a converter is impossible is that the _syntax_ of TeX is Turing complete. If one had kept syntax and programming constructs separated, then a converter would have been possible. (I understand the argument only superficially but I trust Gubinelli enough to report this here).

> Future of TeX?

is TeXmacs, worth trying