David Kastrup <dak@gnu.org> writes:

> Mark H Weaver <mhw@netris.org> writes:
>
>> I can take care of doing this myself, and will of course still credit
>> you in whatever manner you prefer, but I've run into a legal problem: we
>> don't currently have copyright papers for you on file.  Are you willing
>> to file copyright papers for GUILE?
>
> No problems with that.  Standard request-assign?

request-assign.future would be good, which assigns "PAST AND FUTURE
CHANGES".  Is that what you meant by "Standard request-assign"?

> At any rate, here is what I would suggest to create: a function
> min-length receiving a list of lists (possibly as separate arguments via
> a rest argument).
>
> It will return the number of times one can do cdr on every of the given
> arguments until at least one of them turns into a list end with nothing
> turning into anything but a pair or a list end.

I agree that these are reasonable semantics for validation by 'map' and
'for-each'.  I went ahead and implemented it (attached below).  For
efficiency in the common case, I check for cycles in only one list at a
time.  If a cycle is found, the circular list is discarded and cycle
detection begins on another list.  Let me know if you see a way to
improve it.

However, this is not the procedure needed for 'drop-right',
so we'll still need to add a lax variant of length+.  Maybe
'improper-list-length+'?

I guess that both of these new procedures should go in a new module:
(srfi srfi-1 gnu).  We've used this convention for other SRFI
extensions, e.g. (srfi srfi-9 gnu).

    Regards,
      Mark