Using of parse tree externally

[Joe Buck]

> Why does there need to be compiler support for this?  Well, for C++ at
> least and inhertance-based object-oriented languages in general it can
> be extremely difficult to accumulate good cross-referencing
> information external to the compiler.  You just have to duplicate too
> much of the compiler's work.

It should be possible to have some kind of dump format that suffices for
a cross-referencing tool but that lacks sufficient information to
interface external compiler passes to.