siunitx: combine "\num" and "\SI" and change order of arguments

Question

I'm trying to combine the \num and \SI command of siunitx and change the order of the arguments. In particular, what I want to achieve is a new command \Zahl[siunitx-options]<pre-unit>{number}[measure] where everything but number is optional.

The MWE below achieves my objective by copying siunitx internals, which is a bad idea. In particular, I create a new Npn "jorg" based in \SI that changes the order of the original SI command and define \Zahl accordingly. Is there a more consistent and reliable way to achieve the same?

\documentclass{scrartcl}

\usepackage{siunitx,xparse,expl3}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\ExplSyntaxOn
% Create \Zahl based on siunitx' \num and \SI
%  The syntax is then \Zahl[siunitx-options]<pre-unit>{number}[measure]
\cs_new_protected:Npn \__siunitx_jorg:nnnn #1#2#3#4 {
  \IfNoValueTF {#2}
    { \tl_clear:N \l__siunitx_pre_unit_tl }
    {
      \group_begin:
        \__siunitx_unit_in:nn {#2} {#1}
        \cs_set_eq:NN \l__siunitx_pre_unit_tl \l__siunitx_unit_tl
      \exp_args:NNNo \group_end:
      \tl_set:Nn \l__siunitx_pre_unit_tl { \l__siunitx_unit_tl }
    }
  \cs_set_eq:NN \l__siunitx_brackets_bool
    \l__siunitx_multi_brackets_bool
  \__siunitx_combined_unit:nnn {#3} {#4} {#1}
  \__siunitx_combined_output:n {#3}
}

\NewDocumentCommand\Zahl{o D<>{} m O{}}%
 {
  \leavevmode
  \group_begin:
    \IfNoValueTF {#1}
      { \__siunitx_jorg:nnnn { } {#2} {#3} {#4} }
      {
        \keys_set:nn { siunitx } {#1}
        \__siunitx_jorg:nnnn {#1} {#2} {#3} {#4}
      }
  \group_end:
}
\ExplSyntaxOff

\DeclareSIUnit\%{\char37}



\begin{document}

\Zahl{200}

\Zahl{200}[\percent]

\Zahl<£>{200}

\Zahl<£>{200}[\percent]

\Zahl[round-mode=figures,round-precision=3]<£>{200.7}[\percent]

\end{document}

This seems like a situation where using key values instead of optional arguments might be more user-friendly — A.Ellett, Dec 05 '12 at 16:02
I've wondered about a keyval 'pre-unit' argument, but it's not really correct. I also suspect I should have coded the pre-unit part completely separately from the main unit as it's conceptually entirely different. — Joseph Wright, Dec 05 '12 at 17:47

Joseph Wright · Accepted Answer · 2012-12-05T17:56:09.163

You don't need to have a relay function here, as part of the point of xparse is that the code-level functions should 'just work' with the correct number of mandatory arguments.

\documentclass{article}
\usepackage{siunitx}
\ExplSyntaxOn
\NewDocumentCommand \Zahl {o D<>{} m O{}}
  {
    \leavevmode
    \group_begin:
      \IfNoValueTF {#1}
        { \__siunitx_combined:nnnn { } {#3} {#2} {#4} }
        {
          \keys_set:nn { siunitx } {#1}
          \__siunitx_combined:nnnn {#1} {#3} {#2} {#4}
        }
    \group_end:
  }
\ExplSyntaxOff
\begin{document}

\Zahl{200}

\Zahl{200}[\percent]

\Zahl<\pounds>{200}

\Zahl<\pounds>{200}[\percent]

\Zahl[round-mode=figures,round-precision=3]<\pounds>{200.7}[\percent]

\end{document}

There are a few reasons I don't particularly like this idea, from an interface point of view

Trailing optional arguments are not very common in LaTeX2e (certain for general use document commands)
I chose to separate out \num and \SI for a reason :-) (The concepts 'a number' and 'a quantity' are different.)

plus one from a coding point of view

There is not a proper documented code level interface for siunitx (my fault!)

However, it should work well enough. I'm not about to alter the internal interface at the moment, and if I do it will be to provide a documented code-level one.

Thanks, I forgot to ask in the main question: Is there a drawback of \DeclareSIUnit\%{\char37} and using \% instead of \percent for si-numbers? — Jörg, Dec 05 '12 at 17:49
@Jörg No, should be fine: it's just a convention that unit names are words. To be honest, % is an odd one as it's not really a unit, but is in siunitx for reasons of realism :-) — Joseph Wright, Dec 05 '12 at 17:57

siunitx: combine "\num" and "\SI" and change order of arguments

1 Answers1