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Message-ID:  <5256FD2C-CD53-4FF0-A405-5B8B2781E5EC@gmail.com>
Date:         Mon, 14 Mar 2011 09:22:05 +1030
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From: Will Robertson <wspr81@GMAIL.COM>
Subject: Re: expl3's seq_pop_right etc.
To: LATEX-L@listserv.uni-heidelberg.de
In-Reply-To:  <935A1EA2-C971-4A3A-8DF4-6F890E0CFB32@gmail.com>
Precedence: list
Status: R

On 14/03/2011, at 8:44 AM, Will Robertson wrote:

> So I'm generally in favour of this suggestion. But I wonder if there is some downside to using braces that I'm not experienced enough to see. (I can't think off the top of my head of another stack-like data structures in TeX that uses braces.) Can anyone comment further on this?

Well, to answer my own question, here's a function I'm currently using in an expl3 translation of the NFSS: (sorry for the long-ish code chunk)


% \begin{function}{\seq_map_inline:Npn}
% \begin{syntax}
% "\seq_map_inline:Npn" <seq> <params> <function definition>
% \end{syntax}
% Applies the <function definition> to each element of <seq>
% using delimited arguments defined by <params>.
%
% Note that each element is internally delimited so argument matching
% will be `greedy': writing "\seq_map_inline:Npn \foo #1,#2 {[#1,#2]}"
% for element "abc,def" will print `[abc,def]'. Which may or may not seem
% natural to you, depending how familiar you are with \TeX's delimited
% arguments.
%
% For this reason this function is not broadly advertised ":)"
% \end{function}
%
%
% \begin{macro}{\seq_map_inline:Npn}
% When a "seq" contains multiple pieces of information.
% (Perhaps I should be using a "prop" instead; to consider!)
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \seq_map_inline:Npn #1#2# {
  \seq_map_inline_aux:Nnn #1 {#2}
}
\cs_new:Npn \seq_map_inline_aux:Nnn #1#2#3 {
  \cs_set:Npn \seq_elt:w #2 \seq_elt_end: {#3}
  #1 \use_none:n \q_stop
  \cs_set_eq:NN \seq_elt:w \ERROR
}
%    \end{macrocode}
% \end{macro}


Now you could argue that I'm using the wrong data structure here (perhaps a property list would be better) but there you go. I'm not certain we want to support this kind of use, but the current delimited structure of "seq"s sure has come in handy in this particular situation.

Will