Thanks for providing the patch. For me this looks huge and hard to
maintain.

“Hard to maintain”?  How so?

For me this double structure is hard to understand and thus to maintain. YMMV.

Anyhow, if you want me to implement a solution bases on your code, I'll do so. You are far more experienced in Scheme than I am.

-- 
Regards
Hartmut Goebel

| Hartmut Goebel          | h.goebel@crazy-compilers.com               |
| www.crazy-compilers.com | compilers which you thought are impossible |