On 5/12/15, Frank Mittelbach <[log in to unmask]> wrote: > Am 12.05.2015 um 16:34 schrieb Joseph Wright: > >> >> Probably we should add something: as Ulrike says, at the very least >> \prop_show should complain. > > we probably should, but I don't think that \prop_show:N would be the > right place. True, some other "prop" functions do seem to work if you > start from a "c" generated name rather than with \prop_new:N but this is > at best by chance: they are defective and who knows what other defects > are hidden or appear if further "prop" functions are being written. > > So despite the time penalty I think a quick check always that an > argument that should be a "prop" is not equal to \relax is safer. > > frank The problem also comes up with tl (and seq). \RequirePackage{expl3} \ExplSyntaxOn \tl_put_right:cn { l_tl } { \boom } \tl_use:c { l_tl } gives ! TeX capacity exceeded, sorry [input stack size=5000]. \l_tl ->\l_tl \boom But \tl_show:c { l_tl } shows "\l_tl \boom" so experts can understand what's going on. Not sure what should be done, since adding a check to all \tl_put_right:cn seems like a rather large cost. Bruno