Thank you for the prompt and helpful replies. We're embarrassed to report that the problem was far more mundane: a lonely uninitialized integer pointer.
On the bright side, we now have a far deeper understanding of SEXP i/o. Rest assured, the C-coding team (that would be me) has be duly spanked. ubk ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
