[NTG-context] eating up &

[Hans van der Meer]

Hans van der Meer wrote:

> I want to do something with & in (my homemade) tables (making it an  
> active column separator).
> Now I have a macro with two arguments for parameters in Context   
> style:
>
> \def\starttablex{\dodoubleargument\dostarttablex}
> \def\dostarttablex[#1][#2]{%
>
> Now for input:�\starttablex[][] & ... all is well,
> but for input: \starttablex[]� �& ... the ampersand appears to  
> be eaten
> up by the double argument expansion.
>

After some experimenting with argument retrieval I guess I figured  
out what happens here.
Reducing to one optional argument and crippling \dosingleempty to
\def\dosingleempty#1%
   {\noshowargumenterror % \relax % prevents lookahead, brr
    dosinglefakeempty#1}
There is no problem in processing the active &.
Therefore I conclude to the following: on inspecting the next  
character with "\doifnextcharelse[%" the character which is compared  
is the &. Being not equal to [ it is given back but -- if I remember  
well -- there can be a catcode problem. I guess & still functions as  
separator in the \halign template but no longer functions as a macro,  
as it should in my code.

There might be no solution for this within TeX's limitations. But  
maybe you can confirm cq. deny that from your knowledge of TeX (which  
certainly is greater than mine).

Hans van der Meer