Prescript in ConTeXt

Prescript in ConTeXt

[Aditya Mahajan]

Hi Hans and Taco,

I want a command for writing prescript, something that works like
${}^1 f_t$ but with correct spacing. As far as I know, such a command 
does not exist in ConTeXt. A bit of a search shows that the "best" 
definition in LaTeX is by Michael J. Downes 
http://groups.google.com/group/comp.text.tex/msg/49206d0dffe71236?dmode=source&hl=en
This is very similar to \lohi[left] but defined for math mode and 
takes care of math spacing.


\DeclareRobustCommand{\prescript}[3]{%
   \@mathmeasure\z@\scriptstyle{#1}%  put the sup in box 0
   \@mathmeasure\tw@\scriptstyle{#2}% put the sub in box 2
   \ifdim\wd\tw@>\wd\z@
     \setbox\z@\hbox to\wd\tw@{\hfil\unhbox\z@}%
   \else
     \setbox\tw@\hbox to\wd\z@{\hfil\unhbox\tw@}%
   \fi
   % Do not let a preceding mathord symbol approach without any
   % intervening space.
   \mathop{}%
   % Use \mathopen to suppress space between the prescripts and the
   % base object even when the latter is not of type ord.
   \mathopen{\vphantom{#3}}^{\box\z@}_{\box\tw@}%
   #3%
}

To port it to ConTeXt, I need something equivalent to \@mathmeasure, 
which is defined in amsmath.

%  \begin{macro}{\@mathmeasure}
%    The function |\@mathmeasure| takes three arguments; the third arg
%    is typeset as a math formula in an hbox, using arg |#2| as the
%    mathstyle, and the result is left in the box named by the first
%    arg. It is assumed that we are already in math mode, so we can turn
%    off |\everymath| (in particular, |\check@mathfonts|).
%    \begin{macrocode}

\def\@mathmeasure#1#2#3{\setbox#1\hbox{\frozen@everymath\@emptytoks
   \m@th$#2#3$}}


What is the correct way to define mathmeasure in ConTeXt? I do not 
completely understand how math tokens are handled.

Thanks,
Aditya

Re: Prescript in ConTeXt

[Aditya Mahajan]

Actually, I only want a pre superscipt, so the following works for me

\def\presuper#1#2%
   {\mathop{}% To prevent preceeding mathord atoms to approach
    \mathopen{\vphantom{#2}}^{#1}% To prevent space between prescript 
%                                 and next atom.
    \kern-\scriptspace% remove the space introduced by superscript
    #2}


This is not perfect, especially with characters with large left 
"slope" like A. Any suggestions for improving the macro?

Aditya

Re: Prescript in ConTeXt

[Taco Hoekwater]

Aditya Mahajan wrote:
> Actually, I only want a pre superscipt, so the following works for me
> 
> \def\presuper#1#2%
>    {\mathop{}% To prevent preceeding mathord atoms to approach
>     \mathopen{\vphantom{#2}}^{#1}% To prevent space between prescript 
> %                                 and next atom.
>     \kern-\scriptspace% remove the space introduced by superscript
>     #2}
> 
> 
> This is not perfect, especially with characters with large left 
> "slope" like A. Any suggestions for improving the macro?

There is no way to fix that automatically, because TeX does not
have 'italic correction' information for the left-side of a glyph.

Best, Taco