On 14/04/2011 09:44, Will Robertson wrote: > * These should probably be consistent. > * I think returning a quark is dangerous in case of sloppy package authors. If we want consistency between \seq_... and \prop_..., then that is fine but we also need to worry about performance. I'm worried about property lists, as they are used a lot in siunitx. With the short test file \documentclass{article} \usepackage{expl3} \begin{document} \ExplSyntaxOn \prop_new:N \test \tl_new:N \testa \prop_put:Nnn \test { a } { b } \pdfresettimer \prg_replicate:nn { 10000 } { \prop_get:NnN \test { a } \testa \quark_if_no_value:NTF \test { } { } } \showthe\pdfelapsedtime \pdfresettimer \prg_replicate:nn { 10000 } { \prop_if_in:NnTF \test { a } { \prop_get:NnN \test { a } \testa } { } } \showthe\pdfelapsedtime \end{document} I find that the quark-based approach is about twice as fast as using \prop_if_in:Nn. Granted, this is somewhat artificial, but I do essentially this a lot inside siunitx and do not really want to loose speed if I can avoid it. -- Joseph Wright