[metapost] independent variables overflow

[Werner LEMBERG]

> on my hip and modern VISTA and up-to-date MPOST i get
> 
> ! MetaPost capacity exceeded, sorry [independent variables=33554431].
> <for(895.93794)> line:=(1,0)--(1,1)
>                                     ; ENDFOR
> l.153 endfor
>              ;

So I'm not alone with this.  BTW, I'm using the TeXLive SVN from
Jan. 4th, with the GNU/Linux binaries provided in it (which are older
I assume).

What I really don't understand is that I get this overflow at all!
Why is an `:=' assignment handled as an `independent variable' (in
MetaFont parlance), especially if all elements on the right side are
non-variant data elements only?  I looked up the MetaFont source, but
it is too confusing for me...  Or is something different the cause?

I haven't had yet contacted a MetaFont mailing list (assuming that
most experts are reading both lists).

BTW, the warning comes from an addition in `mf.ch', which adds a check
for overflow of the serial numbers.


    Werner