C++ symbolic expression tools?

[est@hyperreal.org]

Kragen discourseth:
>
> Would incremental gc (avoiding intrusive gc pauses) be sufficient for
> your purposes, Eric, or do you need a real real-time gc with absolute
> upper bounds on allocation time?

Ah, Kragen, I'm afraid I need hard real-time..my application domain is
musical. :)

To clarify: I've got a system where several components are
communicating via a protocol that has sexprs as its basic lexical
structure.  Some components are in C++ and need to be able to speak
this protocol.  At the moment, I've thrown some code together such
that I can do things like:

  sexpr s;

  cin >> s;

..however, my implementation is pretty kludgey.  I've been following
lispos for over a year and know there's been interest both in C++
sexpr tools and in sexpr representations of C++ code..thus my
query. :)

I know that (e.g.) rscheme can theoretically be modified to be hard
real-time..but linking that in seems like way more overhead than is
needed.  Also, some of the C++ components of my system will be written
by non-lispers..I really need an easy-to-use library.

E