I'm unsure of whether this would in the end be any more portable than a compilation-based approach. The only fundamental dependencies arc has on plt scheme are on some of its library functions; AFAICT, arc compiles down to fairly portable scheme otherwise. So IMO the best way to make arc portable would be to a) write an arc compiler in arc, b) explicitly separate out the library functions arc needs beyond core r5rs, and c) for each scheme dialect we want to port to, write a support library supplying this functionality.
That's assuming we even want to keep Scheme as the backend, though I don't have any better suggestion. (Well, not yet...)
> It would be portable except it wouldn't work on PLT Scheme, because of inmutable pairs. (isn't that irony?)
Well, arc itself now contains hacked-in mutability for plt's supposedly immutable conses, so that portability problem is fixed :).
