Is there a test for the different styles inside maths mode?

Question

Is there a test for the different styles within maths mode? What I really want is to be able to save the current style to reinvoke it later on, but a \if along the lines of \ifmmode would work just as well.

In the specific example, I want to measure how big something will be when displayed in maths mode, so I do:

\settoheight{\mathheight}{some bit of maths}

except that it complains because the some bit of maths gets put in a box and measured, and the box doesn't know that it's maths. So instead I put:

\settoheight{\mathheight}{\(some bit of maths\)}

except that then I get the wrong answer if this is used in displayed maths. So ideally, I want:

\ifdisplaystyle
 \let\currentstyle\displaystyle
\else
 \iftextstyle
  \let\currentstyle\textstyle
 ...
 \fi
\fi
\settoheight{\mathheight}{\(\currentstyle some bit of maths\)}

and then I'll be happy.

Is there such a test?

---

Okay, so \mathchoice is clearly the way to go (thanks Martin!), but its behaviour is a little odd and since I want to use it to define a macro depending on which mode I'm in, this oddity is quite important. Here's the code:

\newcommand{\mathtest}{%
\gdef\name{a}%
\mathchoice{%
\name
\gdef\name{b}%
}{%
\name
\gdef\name{c}%
}{%
\name
\gdef\name{d}%
}{%
\name
\gdef\name{e}%
}%
\name}

\[
\mathtest
\]

If \mathchoice behaved like \if, this ought to print ab. But it prints ae. All the options to \mathchoice get processed (which makes me wonder a bit how it works, but that's by-the-by).

So, is there an obvious way to make \mathchoice behave a little more like \if?

Answer 1

Lets call such a macro mathsettoheight. I'll keep things simple and define only mathsettoheight (and not mathsettowidth and mathsettodepth).

IIUC, you want this macro to behave like

\mathsettoheight{\dimen}{content}

First, lets consider a simplified version of \settoheight

\def\settoheight#1#2%
  {\setbox\@tempboxa\hbox{{#2}}%
   #1=\ht\@temboxa
   \setbox\@temboxa\box\voidb@x}

The only change that we need to do in \mathsettoheight is to set the box correctly. Instead of

\hbox{#2}

use

\hbox{$\mathpalette{}{#2}$}

\mathpalette is a shortcut used for convenience and is usually defined by all macro packages (plain TeX, LaTeX, ConTeXt) as

\def\mathpalette#1#2{%
  \mathchoice
    {#1\displaystyle{#2}}%
    {#1\textstyle{#2}}%
    {#1\scriptstyle{#2}}%
    {#1\scriptscriptstyle{#2}}}

A minor improvement is to use

\hbox{$\m@th\mathpalette{}{#2}$}

where \m@th sets the math surround to zero (useful if you are interested in the width of the content).

And thats it. The complete definition with you example is

\documentclass{amsart}

\makeatletter

\def\mathsettoheight#1#2%
  {\setbox\@tempboxa\hbox{{#2}}%
   #1=\ht\@temboxa
   \setbox\@temboxa\box\voidb@x}

\def\mathsettoheight#1#2%
  {\setbox\@tempboxa\hbox{$\m@th\mathpalette{}{#2}$}%
   #1=\ht\@tempboxa
   \setbox\@tempboxa\box\voidb@x}

\makeatother

% Test case

\newlength\mathheight
\newcommand*\intheight{%
  \mathsettoheight{\mathheight}{\int}
  \the\mathheight
}


\begin{document}

$\intheight$

\begin{align}
\text{displaystyle}&={\displaystyle\text{\intheight}}\\
 \text{textstyle}&={\textstyle\text{\intheight}} \\
 \text{scriptstyle}&={\scriptstyle\text{\intheight}} \\
 \text{scriptscriptstyle}&={\scriptscriptstyle\text{\intheight}} 
\end{align}

{\obeylines
 \text{displaystyle}= $\displaystyle\text{\intheight}$\\
 \text{textstyle}=$\textstyle\text{\intheight}$ \\
 \text{scriptstyle}=$\scriptstyle\text{\intheight}$ \\
 \text{scriptscriptstyle}=$\scriptscriptstyle\text{\intheight}$ 
\endgraf}

\end{document}

Answer 2

This answer will only apply to LuaTeX and LuaLaTeX, but your question was quite general, so ...

The luatex engine defines a primitive that allows you to query the current math style.

This primitive is called \mathstyle, and when the value is queried (after \ifnum, for example) it returns a number between -1 (not in math mode), 0 (display style), and 7 (cramped scriptscript style).

Luatex also defines four new primitives with \cramped.. prefix: \crampeddisplaystyle, \crampedtextstyle, \crampedscriptstyle, \crampedscriptscriptstyle. These are like their non-prefixed cousins (\displaystyle ... \scriptscriptstyle) except that they explicitly switch to one of the 'cramped' math styles.

Finally, there is the new primitive \Ustack, that is to be used as a prefix for \over.. and \atop.. constructs (which is what commands like \frac and \binom eventually expand into), like so

\Ustack {a \over b}

If you do not do this, \mathstyle will return the wrong value in the initial part of {... \over ...}, as explained by Aditya.

All combined together, these primitives allow code like this:

\ifnum\mathstyle=\textstyle
   \message{normal text style}
\else \ifnum\mathstyle=\crampedtextstyle
   \message{cramped text style}
\fi \fi

and this:

\def\cramped#1% switch the argument to a cramped math style
  {{\ifcase\mathstyle
    \crampeddisplaystyle      \or \or % 0 -> 1
    \crampedtextstyle         \or \or % 2 -> 3
    \crampedscriptstyle       \or \or % 4 -> 5
    \crampedscriptscriptstyle \fi     % 6 -> 7
    #1}}

and even allow you to define a version of \mathchoice that does not typeset everything four times:

\def\mathchoice#1#2#3#4%
  {{\ifcase\mathstyle
    #1\or #1\or
    #2\or #2\or
    #3\or #2\or
    #4\or #4\else #2\fi}}

All this can currently only be used if your underlying engine is luatex, but it is hoped that this extension will eventually become supported by xetex as well.

Answer 3

Yes, you have \mathchoice

\documentclass{article}

\newcommand\mathtest{%
  \mathchoice
  {displaystyle}
  {text style}
  {scriptstyle}
  {scriptscriptstyle}
}

\begin{document}
\[
 \mathtest x^{\mathtest^{\mathtest}}
\]

\(
  \mathtest
\)

\end{document}

Answer 4

Try using package mathstyle http://ctan.org/pkg/mathstyle. This solution is more along the lines of the original question.

\documentclass{article}
\usepackage{mathtools}
\usepackage{mathstyle}
\usepackage{calc}

\newlength\mathheight
\newcommand*\intheight{%
  \settototalheight{\mathheight}{$\currentmathstyle\int$}
  \the\mathheight
}

\begin{document}

\begin{align}
 \text{displaystyle}&={\displaystyle\text{\intheight}}\\
 \text{textstyle}&={\textstyle\text{\intheight}} \\
 \text{scriptstyle}&={\scriptstyle\text{\intheight}} \\
 \text{scriptscriptstyle}&={\scriptscriptstyle\text{\intheight}} 
\end{align}

\end{document}

Answer 5

Here it comes a late late solution which, by the way, hasn't been tested thoroughly, but works in the case of what OP intended to do.

It's semiexpandable, i.e., the macro \def\mathcase{\getmsty\mstycase} has two parts \getmsty which is not expandable, and \mstycase which is indeed expandable. Similar, e.g., to \pgfmathparse{..} and \pgfmathresult. For instance, if you want to put something inside a csname you would need \getmsty\csname\mstycase{cdot}{times}{div}{cdots}\endcsname.

Any comment is welcome, because this might not work as expected, at least as I intended.

\documentclass{scrartcl}

\usepackage{mathtools}


\usepackage{zref-savepos}
\newcount\mmstynum
\newcount\tmpnum
\protected\def\getmsty
 {\global\advance\mmstynum1 %
  \expandafter\getstyA\expandafter{\number\mmstynum}}
\protected\def\getstyA#1%
 {\zsaveposx{mmsty-#1-a}%
  \mathchoice{\kern4sp}{\kern3sp}{\kern2sp}{\kern1sp}%
  \zsaveposx{mmsty-#1-b}
  \tmpnum=\numexpr
            \zposx{mmsty-#1-b} - \zposx{mmsty-#1-a}
          \relax
   \ifcase\tmpnum\or\kern-1sp \or\kern-2sp \or\kern-3sp \or\kern-4sp \fi}
\protected\def\mstycase
 {\ifcase\tmpnum\expandafter\gobblefour\or\expandafter\usefourth\or
   \expandafter\usethird\or\expandafter\usesecond\or
   \expandafter\usefirst\else\expandafter\gobblefour\fi}
\protected\def\mathcase{\getmsty\mstycase}

\long\def\gobblefour#1#2#3#4{}
\long\def\usefourth#1#2#3#4{#4}
\long\def\usethird#1#2#3#4{#3}
\long\def\usesecond#1#2#3#4{#2}
\long\def\usefirst#1#2#3#4{#1}


\def\tmpa{If this prints it means it doesn't work}
\newcommand*\foo
 {\mathcase % compare with \mathchoice
   {\def\tmpa{displaystyle}}
   {\def\tmpa{textstyle}}
   {\def\tmpa{scriptstyle}}
   {\def\tmpa{scriptscriptstyle}}
  \text\tmpa}

\begin{document}

\begin{align}
 \text{displaystyle} &= {\displaystyle\foo}\\
 \text{textstyle} &= {\textstyle\foo} \\
 \text{scriptstyle} &= {\scriptstyle\foo} \\
 \text{scriptscriptstyle} &= {\scriptscriptstyle\foo} 
\end{align}

\end{document}

Or… may be this solution doesn't work because of how it calculates the current style, it might not be robust (which is done by adding a small space and then checking with \pdfsavepos the space that has been inserted).

Answer 6

The OP states, "What I really want is to be able to save the current style to reinvoke it later on". The method I described in my answer at Proper use of \mathchoice has been incorporated into my scalerel package under the syntax \ThisStyle{...\SavedStyle...}. When one wishes to save the current math style, issue a \ThisStyle{} at that point. Then place all the messy boxed stuff inside the argument, and whenever "this style" needs to be recalled, issue a \SavedStyle inside the \ThisStyle argument.

A most simple example is given in the MWE below, showing that script (or scriptscript) style can be remembered inside of an \fbox and recalled.

\documentclass{article}
\usepackage{scalerel}
\begin{document}
\def\tmp{\ThisStyle{\fbox{$\SavedStyle 1+y$}}}
$\tmp\quad 
X_{\tmp}\quad 
Z_{X_{\tmp}}$
\end{document}

It is good to remember that this approach utilizes a \mathchoice approach to implementation, but can often save a lot of typing relative to the \mathchoice syntax.