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I am using quite a lot of notation in my text. Thus, I decided to write some commands such as:

\newcommand{\struct}[1]{\mathsf{#1}}

The typical use is as follows:

Let $(\struct{A}_n)$ be a sequence of structures.

Notice that the subscript is outside the struct command.

My problem lies in the fact that I need to 'place' the exact name of the object to various places. That is, to write something as long description of the structure:

(\struct{A}_n, S_{\struct{A}_n}, R_{\struct{A}_n})

See that I cannot just write a command like this:

\newcommand{\longstruct}[1]{(\mathsf{#1}, S_\mathsf{#1}, R_\mathsf{#1})}

and use it similarly:

Let $(\longstruct{A}_n)$ be a sequence of structures.

because the subscript _n would be in the wrong place.

As a solution, it would work being able to handle the 'base' of the name and subscript/superscript separately. For example in a command like this:

% #1 Base
% #2 Subscript
% #3 Superscript
\newcommand{\longstruct}[3]{(\mathsf{#1}_{#2}^{#3}, S_{\mathsf{#1}_{#2}^{#3}}, R_{\mathsf{#1}_{#2}^{#3}})}

However it feels too cumbersome to be used in code. Optional parameters help, but it is still not optimal.

How I would like to use the command:

Let $(\longstruct{A_n})$ be a sequence of structures.

But of course, as only A is supposed to go in \mathsf{.}, the argument needs to be parsed into the base and subscript/superscript inside the command.

Is there a way how to do that?

Note: I'm still rather an inexperienced latex user and it is quite likely that there is a better solution, which didn't even crossed my mind. I'm open to any suggestions. Thank you.

Edit: The superscripts are indented to be used as in the command example with three parameters yielding the result such as this:

(\struct{A}_n^d, S_{\struct{A}_n^d}, R_{\struct{A}_n^d})
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  • Wouldn't \longstruct{A}{n} be simpler to implement? Commented Apr 7, 2022 at 11:02
  • It probably would. But sometimes a superscript needs to be used as well and sometimes none of them and the 'parsing' way would make the use more clear. Of course, from the practical point of view, it is probably the way to go. Commented Apr 7, 2022 at 11:08
  • I posted an implementation, but accommodating superscripts would need an example of the intended usage. Commented Apr 7, 2022 at 11:16
  • Thank you, I updated the post. Commented Apr 7, 2022 at 11:39

1 Answer 1

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You can do it with \NewDocumentCommand, that's able to split the argument at a given token.

\documentclass{article}
\usepackage{amsmath}

\NewDocumentCommand{\struct}{m}{\mathsf{#1}}

\NewDocumentCommand{\longstruct}{>{\SplitArgument{1}{_}}m}{%
  (\makelongstruct#1)%
}

\NewDocumentCommand{\makelongstruct}{mm}{%
  \struct{#1}\IfValueT{#2}{_{#2}},%
  S_{\struct{#1}\IfValueT{#2}{_{#2}}},%
  R_{\struct{#1}\IfValueT{#2}{_{#2}}}%
}

\begin{document}

$\longstruct{A_n}$

$\longstruct{B}$

\end{document}

enter image description here

Explanation: with \SplitArgument{1}{_} the argument A_n becomes {A}{n} and we can pass it to an auxiliary command. If the _ is missing, we get {A}{-NoValue-} and this can be tested in order to avoid adding the subscript.

We can also accommodate superscripts:

\documentclass{article}
\usepackage{amsmath}

\NewDocumentCommand{\struct}{m}{\mathsf{#1}}

\NewDocumentCommand{\longstruct}{>{\SplitArgument{1}{_}}m}{%
  (\makelongstructA#1)%
}

\NewDocumentCommand{\makelongstructA}{mm}{%
  \IfNoValueTF{#2}{% no subscripts
    \makestruct{#1}{\kern-\scriptspace}{\kern-\scriptspace}%
  }{% there are subscripts
    \makelongstructB{#1}{#2}%
  }%
}

\NewDocumentCommand{\makelongstructB}{
  >{\SplitArgument{1}{^}}m
  >{\SplitArgument{1}{^}}m
}{%
  \makelongstructC#1#2%
}

\NewDocumentCommand{\makestruct}{mmm}{%
  \struct{#1}\IfValueT{#2}{_{#2}}\IfValueT{#3}{^{#3}},%
  S_{\struct{#1}\IfValueT{#2}{_{#2}}\IfValueT{#3}{^{#3}}},%
  R_{\struct{#1}\IfValueT{#2}{_{#2}}\IfValueT{#3}{^{#3}}}%
}

\NewDocumentCommand{\makelongstructC}{mmmm}{%
  \IfValueTF{#2}{% we had A^s_n
    \makestruct{#1}{#3}{#2}%
  }{% we had A_n^s
%\showtokens{#1,#2,#3}
    \makestruct{#1}{#3}{#4}%
  }%
}

\begin{document}

$\longstruct{A_n}$

$\longstruct{B}$

$\longstruct{C_n^k}$

$\longstruct{D^k_n}$

\end{document}

enter image description here

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3
  • Thank you for the code and the explanation. However, I don't know how to generalize this for handling the superscripts as well. It seems that the \SplitArgument takes just a single token (if would be handy to pass both _ and ^). Perhaps a repeated use of \SplitArgument can be used? Commented Apr 7, 2022 at 11:42
  • @TomášHons I added the version supporting superscripts Commented Apr 7, 2022 at 15:39
  • Thank you a lot! These are valuable tricks. Commented Apr 7, 2022 at 19:38

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