Message-Id: <9306211122.AA11581@sc.zib-berlin.dbp.de>
Reply-To: Mailing list for the LaTeX3 project <LATEX-L@vm.urz.Uni-Heidelberg.de>
Date:         Mon, 21 Jun 93 12:16:46 BST
From: P.TAYLOR@RHBNC.AC.UK
Sender: Mailing list for the LaTeX3 project <LATEX-L@vm.urz.Uni-Heidelberg.de>
To: Multiple Recipients of <LATEX-L@vm.urz.Uni-Heidelberg.de>
Subject:      RE: adding fake registers to ltx3
Status: R


[Additional registers in LaTeX-3]

I understand Frank's response (which I will not cite here in order to keep
length down), and I thank him for explaining current policy in such detail.
But I wonder if there is any merit in a scheme such as the following:

	Reserve $n$ registers for `normal' use;
	Associate the remaining registers with a potentially infinite
		set of `structures', as in:

	\newstruct \myregisters %%% associates the `pooled' registers with
	      			%%% \myregisters, providing a fast store/recall
	      			%%% mechanism.

	\with \myregisters 	%%% \myregisters becomes `current \with context'
	\do   \begin		%%% pre-loads from `current \with context'
	       ...		%%% everything you'd normally do with registers
	      \end		%%% save register set in `current \with context'


This could allow very elegant module implementation, but a means would need
to be provided to permit intermodule communication.  In effect, one would
want to be able to write:

	      \myregisters.\skip 19 = \hisregisters.\skip 21

and, of course, far more complex variants thereof, including the standard
TeX features of implicit multiplication for <factor><skip or dimen> and
implicit concatenation for <prefix><count>.  But to accomplish this would
require pre-loading and post-storing of the selected registers in the register
pool associated with \myregisters and \hisregisters respectively, and this
would interfere with the assignments in a totally destructive way; therefore
I suggest we probably need a \assign command which would parse the expression,
evaluate the terms, and then perform the necessary loads, assignments and
stores, as in:

	      \assign {\myregisters.\skip 19 = \hisregisters.\skip 21}

One could also imagine a more efficient form of the \newstruct declaration which
would allow only a limited number of registers associated with the structure
variable, and perhaps type-restricted structures for even further efficiency.
For example, rather than reserve space for a full set of registers of all types,
one could list the registers to be associated with a particular structure:

	      \newstruct \myregisters {\toppageskip, \itemcount, \margindimen}

The \with ... \begin ... \end construct would then only need to restore and
save the named registers.

All of these are very tentative ideas, and I openly confess I have not fully
thought them through; but do others think there might be any merit in so doing?

	      				Philip Taylor, RHBNC