siunitx: spacing between \num and a variable name

Question

I am using siunitx to typeset numbers and units. But when typesetting numbers in front of a variable, I feel a thin space is missing.

For example, with \num{0.1234}a I get (1), and with \num{0.1234}\,a I get (2) which looks better. Is there a way to automate this or do I have to manually put a thin space after each number?

Answer 1

I defined \mynum for you which checks if the next token is of catcode “letter”.

\documentclass{article}
\usepackage{siunitx}
\ExplSyntaxOn

\NewDocumentCommand \mynum { o m }
 {
  \num [ #1 ] { #2 }
  \peek_catcode_ignore_spaces:NT \c_catcode_letter_token { \, }
 }

\ExplSyntaxOff
\begin{document}
Normal behaviour (very recommended)
\begin{equation}
  \num{0,1234}\,a
\end{equation}
Desired behaviour
\begin{equation}
  \mynum{0,1234}a
\end{equation}
\end{document}

---

You can also override the \num command provided by siunitx, which is not recommended. Therefore, I copied the definition of \num from siunitx.sty and appended the relevant bits.

\documentclass{article}
\usepackage{siunitx}

\ExplSyntaxOn

\RenewDocumentCommand \num { o m }
 {
  % begin from siunitx.sty
  \leavevmode
  \group_begin:
   \IfNoValueF {#1}
    { \keys_set:nn { siunitx } {#1} }
   \__siunitx_number_output:n {#2}
  \group_end:
  % end from siunitx.sty
  \peek_catcode_ignore_spaces:NT \c_catcode_letter_token { \, }
 }

\ExplSyntaxOff

\begin{document}
$\num{0,1234}a$
\end{document}