[texhax] Parsing ^ and _

[Alex Scorpan]

> Is there any simple way of parsing ^ and _ that mimics what TeX  
> does, but
> allows other procedures than just putting in super and subscripts?   
> For
> example, I have a \to procedure that replaces the plain tex (which  
> is a
> synonym for \rightarrow) and measures the sizes of the scripts and  
> uses
> that information to choose the length of the arrow.  As it is, I  
> can use
> any of \to^{...}, \to_{...}, \to^{...}_{...} but not \to_{...}^ 
> {...}.  I
> already have three uses of \@ifnextchar and the only way I can  
> think to
> implement allowing all four would use several more.  Is there a  
> simpler
> way of doing this.


On one hand, \xrightarrow[bottom]{top} does pretty much what you want  
in amsmath.

The simplest (but rather rigid) way could be
	\def\to^#1_#2{\xrightarrow[#2]{#1}}
but you'd need both a super- and subscript, in the order used in  
\def, as in
	\[ A\to^{top}_{bottom}B \]

-- Alex