Hey Tom,
You need to define a lang_tree_node type, even if its empty. See
the lto frontend example.
You could also look at this site
(http://code.redbrain.co.uk/cgit.cgi/gcc-dev/tree/gcc/gcalc?h=documentation).
It contains the front-end code for a very simple front-end showing the
general/expected structure of the front-end. The code isn't yet optimal,
but it should help you to figure out what you really need to build-up
the front-end.
If you have any specific questions about front-ends and how to pass data
to the middle-end feel free to ask on this list :-)
Hope that helps,
Andi
