# Passing multiple arguments from ProcessList (xparse) to a macro. Result to be used in tabular

I am making a macro that will take user input of a grading scheme and place it into a tabular environment. I would like the syntax to be as simple as possible and decided on:

\tabulate{ eval1,%1 ; eval2,%2 ; ... ; evaln,%n}

as the input scheme, e.g.

\tabulate{Midterm 1,15\% ; Midterm 2,20\%}

Having asked question about building a table from a macro previously, I know that I should (need to?) use toks to build the rows of the table. My first attempt was the following:

\documentclass{article}
\usepackage{xparse}

\makeatletter
\newtoks\@tabtoks
\newcommand*\resettabtoks{\@tabtoks{}}
\newcommand*\printtabtoks{\the\@tabtoks}
\makeatother

\DeclareDocumentCommand \tabulate%
{ > { \SplitList { ; } } m }%
{\ProcessList {#1} {\mycommand}}

It took me a while to sort of figure out why this didn't work: the #1 is passed from ProcessList to mycommand as a single token and can't be read as individual tokens? Question: Is my understanding of why the above doesn't work reasonably correct? If not, could someone please clarify? Based on that fuzzy understanding, I came up with a solution that works but deviates from my desired input scheme (this is the almost working example):

\documentclass{article}
\usepackage{xparse}

\makeatletter
\newtoks\@tabtoks
\newcommand*\resettabtoks{\@tabtoks{}}
\newcommand*\printtabtoks{\the\@tabtoks}
\makeatother

\DeclareDocumentCommand \tabulate%
{ > { \SplitList { ; } } m }%
{\ProcessList {#1} {\mycommand}}
\newcommand{\mycommand}[1]{
\def\temp{#1}
\expandafter\mycommandTwo\temp
}

%{\ProcessList {#1} {\mycommand}}

\begin{document}

\resettabtoks
\tabulate{Midterm 1,{15\%};Midterm 2,{20\%};Midterm 3,{25\%}}

\begin{tabular}{cc}
\printtabtoks
\end{tabular}

\end{document}

Again, based on my fuzzy understanding, I stored the argument from ProcessList in a macro that gets expanded and can therefore be read as individual tokens by mycommandTwo. Depending on whether I understood the initial problem correctly, this may not be the correct interpretation. My problem is that without grouping the percentages as above, ie. {15\%} rather than just 15\% I don't get the output that I want. I'm not sure why that is the case. Could anyone help me understand why the percentages need to be grouped and/or suggest a possible fix/improvement on what I currently have. My previous attempt involved parsing the csv eval,%, prepending each entry with an &, and then deleting the first & in the resulting list but I couldn't make it work. Thanks in advance!

Edit 1: Thinking about it now, I would prefer to insulate the user from even needing to enter the \ prior to the %'s, although I suspect that would require more knowledge than I have.

-
Why didn't do use the expl3-syntax? See: texdev.net/2012/04/29/programming-latex3-more-on-expansion – Marco Daniel May 8 '12 at 19:37
@MarcoDaniel Thanks for the link, I will certainly have a read :) However, at the moment I am completely unfamiliar with the new syntax. I intend to start learning it soon, but felt that it might be a little much to take on for this project. Once I have a working "Course Outline Package" and fewer time constraints, I'll go through it and try to learn the new syntax by re-implementing my macros with it. When doing that, would this be the appropriate place to start? texdev.net/2011/12/07/programming-latex3-background – Scott H. May 8 '12 at 19:52
You also might want to read interface3 if you're interested in expl3 – clemens May 8 '12 at 20:28
Didn't read carefully enough to be sure, but couldn't \DeclareDocumentCommand{\tabulate}{m}{\tl_set:Nn \l_scott_tmpa_tl {#1} \tl_replace_all:Nnn \l_scott_tmpa_tl {;} {\\} \tl_replace_all:Nnn \l_scott_tmpa_tl {,} {&} \tl_use:N \l_scott_tmpa_tl}, to be used as \begin{tabular}{cc} \tabulate{a,b;c,d} \end{tabular} work? – Bruno Le Floch May 20 '12 at 22:31
@BrunoLeFloch Yes, that is a nice clean solution and works quite well! – Scott H. May 21 '12 at 19:46

When doing tabular things, the moment when TeX sees the & is crucial and it's best to collect in advance the data and present it to TeX once.

Here's a way that uses expl3 syntax:

\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand{\tabulate}{ O{cc} m }
{
\tl_clear:N \l_scott_body_tl
\seq_set_split:Nnn \l_scott_body_seq { ; } { #2 }
\seq_map_inline:Nn \l_scott_body_seq { \scott_do_line:n { ##1 } }
\begin{tabular}{#1}
\tl_use:N \l_scott_body_tl
\end{tabular}
}
\cs_new:Npn \scott_do_line:n #1
{
\tl_clear:N \l_scott_row_tl
\clist_map_inline:nn { #1 } { \tl_put_right:Nn \l_scott_row_tl { & ##1 } }
\tl_put_right:Nn \l_scott_row_tl { \\ }
\tl_set:Nx \l_scott_row_tl { \tl_tail:N \l_scott_row_tl }
\tl_put_right:NV \l_scott_body_tl \l_scott_row_tl
}
\seq_new:N \l_scott_body_seq
\tl_new:N \l_scott_body_tl
\tl_new:N \l_scott_row_tl
\ExplSyntaxOff
\begin{document}

\tabulate{Midterm 1,{15\%};Midterm 2,{20\%};Midterm 3,{25\%}}

\tabulate[cr]{Midterm 1,{15\%};Midterm 2,{20\%};Midterm 3,{5\%}}

\end{document}

One might do with \ProcessList, at least for getting the rows:

\ExplSyntaxOn
\NewDocumentCommand{\tabulate}{ O{cc} >{ \SplitList { ; } } m }
{
\tl_clear:N \l_scott_body_tl
\ProcessList { #2 } { \scott_do_line:n }
\begin{tabular}{#1}
\tl_use:N \l_scott_body_tl
\end{tabular}
}
\cs_new:Npn \scott_do_line:n #1
{
\tl_clear:N \l_scott_row_tl
\clist_map_inline:nn { #1 } { \tl_put_right:Nn \l_scott_row_tl { & ##1 } }
\tl_put_right:Nn \l_scott_row_tl { \\ }
\tl_set:Nx \l_scott_row_tl { \tl_tail:N \l_scott_row_tl }
\tl_put_right:NV \l_scott_body_tl \l_scott_row_tl
}
\tl_new:N \l_scott_body_tl
\tl_new:N \l_scott_row_tl
\ExplSyntaxOff

This is essentially the same as before: \SplitList splits the argument into a sequence and then \ProcessList does a mapping to this sequence (which is what is done directly in the first version).

Each row is processed as a clist; each item is preceded by &, a row is stored in a token list and the first & is pruned off. Then each row is added to a "body" token list, which is then delivered to the tabular environment.

If you really want to allow % directly, then you can use a common trick:

\newcommand{\tabulate}{\begingroup\catcode`\%=12 \innertabulate}

and then define \innertabulate just like \tabulate before, but adding \endgroup at its end.

-
Thank you for taking the time to help. The inclusion of the tabular parameters was a nice touch, as was the tip for allowing %. – Scott H. May 8 '12 at 23:16

The \SplitList in this command

\DeclareDocumentCommand \tabulate { > { \SplitList { ; } } m }%
{\ProcessList {#1} {\mycommand}}
\tabulate{Midterm 1,15;Midterm 2,20;Midterm 3,25}

will give {Midterm 1,15}{Midterm 2,20}{Midterm 3,25} for #1 so indeed the single items are single tokens from the perspective of a macro.

Your attempt has another problem. Consider this command:

\def\test#1,#2{1: #1; 2: #2; that's it! }
\test Midterm,15\%

will give you

1: Midterm; 2: 1; that's it! 5%

Only the first token after the comma is seen. That's why you have to add the braces around 15\%.

In order to see the whole thing you'll need another marker:

\def\test#1,#2\stop{1: #1; 2: #2; that's it! }
\test Midterm,15\%\stop

IMHO the easiest thing to do would be to use expl3's mapping functionality:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\tl_new:N \l_tab_interior_tl
% this maps through the token list created by \SplitList and will apply
% \add_to_tab:w to every item in a way that it doesn't have to contain the
% comman and the secoind argument:
\DeclareDocumentCommand \tabulate { > { \SplitList { ; } } m }
{ \tl_map_inline:nn { #1 } { \add_to_tab:w ##1,, \q_stop } }

% this adds every entry from above in the form #1 & #2\% \\ to the token list
% that builds the table; it works similar to the \def\test above:
\cs_new:Npn \add_to_tab:w #1,#2,#3 \q_stop
{
\tl_put_right:Nn \l_tab_interior_tl
{ #1 & \tl_if_blank:nF { #2 } { #2 \% } \\ }
}

% this prints the actual table material:
\cs_new_nopar:Npn \writetable { \tl_use:N \l_tab_interior_tl }

% this clears the tabular material; this functionality could of course be added
% to the \writetable command if you're sure you're not going to use it twice:
\cs_new_nopar:Npn \cleartable { \tl_clear:N \l_tab_interior_tl }
\ExplSyntaxOff

\begin{document}

\tabulate{Midterm 1,15;Midterm 2,20;Midterm 3,25}

\begin{tabular}{cc}
\writetable
\end{tabular}

\cleartable
\tabulate{Midterm 1;Midterm 2,20;Midterm 3}

\begin{tabular}{cc}
\writetable
\end{tabular}

\end{document}
-
While I accepted egreg's answer above, I appreciate very much the time you took to answer, and in particular the time you took to explain my errors and to comment your code. Both answers completely solved my problem but in different ways and since I couldn't decide which was objectively "better", I went with the one that came first. I spent quite a bit of time perusing meta questions to see if I could reward you in some way, but unfortunately it seems that my thanks will need to suffice. – Scott H. May 8 '12 at 23:22
@Scott You're welcome. Upvoting is thanks enough :) – clemens May 9 '12 at 4:47