LaTeX is a full programming language. Parsing it means executing the program.
While it seems to be simple in many of the common cases - \section
etc. - it is by far not trivial. In fact, it should be turing complete. And some parts will even have a more or less different syntax. Take TIKZ for example - an excellent graph drawing library for LaTeX. It's syntax is somewhat like latex, but other parts are more that of modern programming languages. And a lot is like stylesheets.
However, you might be able to get away with supporting just part of the latex syntax. Have a look at what Texlipse does. It's in Java.