[texhax] plain TeX: `No room for a new \fam'

[Donald Arseneau]

On Tue, July 9, 2013 2:11 am, Philip Taylor wrote:
>
> Donald Arseneau wrote:
>
>> The way to "get round" it is to assign some dynamically, locally
>> within the math, rather than globally.
>
> Is it not the case, Donald (and I ask this from memory, so
> may well be mistaken) that maths families are evaluated
> only at the very end of the maths formula,

It is more complicated than that. some aspects need to be known
as the math list is read, so each fam needs to be assigned before
use and must persist to the end.

> so locally-defined families

OK, I was speaking of local to a formula, but not local to a portion
within the formula.  If you need more than 16 families in a single
formula, you are out of luck, or portions...

> would have to be encapsulated in non-maths
> lists such as hboxes, vboxes, etc

That brings up a complication I missed though: You can't use TeX
grouping to ensure locality, because sub-formulas are in groups
and so truly local assignments won't persist until the end of the
math.  An on-demand assignment implementation would have to use
messy global assignments and manual forgetting.


Donald Arseneau, TRIUMF CMMS, asnd at triumf.ca