[r6rs-discuss] [Formal] Requirement to detect circular lists

[AndrevanTonder]

Sorry to be a pest, but I am wondering why introduce
the whole machinery of plausible lists at all?

If I understand correctly, the intended semantics
of (map f x) can be stated much more simply as:

   - Implementations of map are required to check whether
     x is a list before the first application
     of f.  If x is not a list, an exception must
     be raised.

This check is decidable (ignoring concurrency, as one
should, since r6rs Scheme does not have concurrency).
No extra section is needed to describe this...

Cheers
Andre