Thanks, Alex. That might be good enough for me for this particular concern; in the absence of a language specification specifying my behaviour and referring to precedent seems like a reasonable fall back. Dan On Tue, 2020-09-08 at 09:33 +0200, Bertram, Alexander wrote:> Hi Dan, > > For what it's worth, Renjin requires LISTSXPs to hold either a > LISTSXP or a NULL, and this appears to be largely the case in > practice based on running tests for thousands of packages (including > cross compiled C code). I can only remember it being briefly an issue > with the rlang package, but Lionel graciously changed it: > https://github.com/r-lib/rlang/pull/579 > > Best, > Alex