[NTG-context] Macros which scan subscripts/superscripts in ConTeXt

[Hans Hagen]

On 6/26/2020 3:47 AM, Aditya Mahajan wrote:
> On Thu, 25 Jun 2020, Jairo A. del Rio wrote:
> 
>> Hi, list! I've seen the following in Stack Exchange:
>>
>> https://tex.stackexchange.com/questions/503208/define-macro-that-scans-ahead-for-super-and-or-subscript-absorbs-them-and-mo 
>>
>>
>> The answer is:
>>
>> \documentclass{article}\usepackage{amsmath}\usepackage{xparse}
>> \NewDocumentCommand{\mymathsym}{e{^_}}{%
>>  x^{\mathrm{foo}\IfValueT{#1}{,#1}}_{\mathrm{bar}\IfValueT{#2}{,#2}}%}
>> \begin{document}
>> \begin{gather}\mymathsym \\\mymathsym^{\mathrm{extrasup}}
>> \\\mymathsym_{\mathrm{extrasub}}
>> \\\mymathsym^{\mathrm{extrasup}}_{\mathrm{extrasub}}
>> \\\mymathsym_{\mathrm{extrasub}}^{\mathrm{extrasup}}   \end{gather}
>> \end{document}
>>
>> Such a macro contextually defines a behavior for a subscript and a
>> superscript even if they aren't displayed in a specific order, so
>>
>> \mymacro_{a}^{b}
>>
>> \mymacro^{b}_{a}
>>
>>
>> have the same output, even if the intended behavior is not the typical
>> one (I could redefine it so subscripts change colors, for instance).
>> Although I could just port the macro using xparse-generic because it
>> works in ConTeXt too, how to define a macro like that the ConTeXt way,
>> i.e., using only ConTeXt macros?
> 
> Return of the dodo :-)
> 
> % Must be outside \unprotect .. \protect so that _ has usual catcodes
> \def\capturemathoplimits#1%
>    {\doifnextcharelse _%
>      {\docapturemathoplimitsA{#1}}
>      {\doifnextcharelse ^%
>        {\docapturemathoplimitsB{#1}}
>        {\redocapturemathoplimits{#1}}}}
> 
> \def\docapturemathoplimitsA#1#2#3%
>    {\doifnextcharelse ^%
>      {\dodocapturemathoplimitsA{#1}{#2}{#3}}
>      {\dodocapturemathoplimitsA{#1}{#2}{#3}\empty\empty}}
> 
> \def\dodocapturemathoplimitsA#1#2#3#4#5{#1{#5}{#3}}
> 
> \def\docapturemathoplimitsB#1#2#3%
>    {\doifnextcharelse _%
>      {\dodocapturemathoplimitsB{#1}{#2}{#3}}
>      {\dodocapturemathoplimitsB{#1}{#2}{#3}\empty\empty}}
> 
> \def\dodocapturemathoplimitsB#1#2#3#4#5{#1{#3}{#5}}
> 
> \def\redocapturemathoplimits#1{#1\empty\empty\empty\empty\empty}
> 
> 
> % Usage:
> 
> \define\mymacro{\capturemathoplimits\domymacro}
> 
> \def\domymacro#1#2%
>    % #1 is supscript, #2 is subscript
>    
> {x^{\mathrm{foo}\doifsomething{#1}{,#1}}_{\mathrm{bar}\doifsomething{#2}{,#2}}} 
> 
> 
> \starttext
> \startlines
> $\mymacro$ $\mymacro^{\mathrm{extrasup}}$
> $\mymacro_{\mathrm{extrasub}}$ 
> $\mymacro^{\mathrm{extrasup}}_{\mathrm{extrasub}}$ 
> $\mymacro_{\mathrm{extrasub}}^{\mathrm{extrasup}}$ \stoplines
> \stoptext
We could have this:

\unexpanded\def\scripts
   {\scratchtoksone\emptytoks
    \scratchtokstwo\emptytoks
    \doscriptscheck}

\def\doscriptscheck
   {\doifnextcharelse _%
      \doscriptssub
      {\doifnextcharelse ^%
         \doscriptssup
         \doscriptsflush}}

\def\doscriptsflush
   {\doifsometoks\scratchtoksone{^{\the\scratchtoksone}}%
    \doifsometoks\scratchtokstwo{_{\the\scratchtokstwo}}}

\def\doscriptssup ^#1%
   {\doifelsesometoks\scratchtoksone
      {\appendtoks,{#1}\to\scratchtoksone}
      {\scratchtoksone{{#1}}}%
    \doscriptscheck}

\def\doscriptssub _#1%
   {\doifelsesometoks\scratchtokstwo
      {\appendtoks,{#1}\to\scratchtokstwo}
      {\scratchtokstwo{{#1}}}%
    \doscriptscheck}

% % a bit more low level:

% \unexpanded\def\scripts
%   {\scratchtoksone\emptytoks
%    \scratchtokstwo\emptytoks
%    \doscriptscheck}
%
% \def\doscriptscheck
%   {\doifnextcharelse ^%
%      {\doscriptsstep\scratchtoksone}
%      {\doifnextcharelse _%
%         {\doscriptsstep\scratchtokstwo}
%         {\doscriptsflush}}}
%
% \def\doscriptsflush
% 
{\iftok\scratchtoksone\emptytoks\else\Usuperscript{\the\scratchtoksone}\fi%
%    \iftok\scratchtokstwo\emptytoks\else\Usubscript 
{\the\scratchtokstwo}\fi}
%
% \def\doscriptsstep#1#1#3%
%   {\etoksapp#1{\iftok#1\emptytoks\else,\fi\normalunexpanded{#3}}%
%    \doscriptscheck}

\starttext
\startlines
$z\scripts _{\rm one} _{\bf two} ^{one} _{ three} ^{\bi two}$
\stoplines
\stoptext


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