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            <58AFBC3A-4209-4BC0-BB3A-5B14D6B5EFD8@gmail.com>
            <4DA727A9.2050903@morningstar2.co.uk>
Message-ID:  <19880.43516.366891.822111@morse.mittelbach-online.de>
Date:         Fri, 15 Apr 2011 22:26:36 +0200
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From: Frank Mittelbach <frank.mittelbach@LATEX-PROJECT.ORG>
Subject: Re: The nature of popping from an empty sequence
To: LATEX-L@listserv.uni-heidelberg.de
In-Reply-To:  <4DA727A9.2050903@morningstar2.co.uk>
Precedence: list
Status: R

Joseph Wright writes:
 > 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.

right let's worry about performance (you know I do that quite often :-)

 > 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}

well try this one as well which is what I was thinking of (kind of):

\cs_new:Npn \prop_get:NnNF #1#2#3#4 {
  \prop_get:NnN #1 {#2} #3
  \quark_if_no_value:NF 
     {
       \cs_set_eq:NN #3 \c_undefined 
       #4
     }
} 

  \pdfresettimer
  \prg_replicate:nn { 50000 }
    {
       \prop_get:NnNF \test { a } \testa 
                      { }
    }
  \showthe\pdfelapsedtime

 > 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.

basically it tells us that \prop_if_in:Nn is fairly inefficient and that in
turn is due to it using \quark_if_no_value:nTF I guess. Saving the result and
then checking it is much much faster. Perhaps that implementation should
change.

frank