[XeTeX] [tex-implementors] Proposal : that TeX engines generating PDF directly should be able to close the output file without terminating.

[Ross Moore]

Hi Jonathan,

On 4 Jul 2020, at 8:55 am, Jonathan Kew <jfkthame at gmail.com<mailto:jfkthame at gmail.com>> wrote:

On 03/07/2020 20:13, Bruno Le Floch wrote:
On 7/3/20 6:50 PM, Jonathan Kew wrote:
On 03/07/2020 16:26, Philip Taylor wrote:
Jonathan Kew wrote:

Many potential use-cases, I think, can be equally well addressed by multiple TeX
invocations under the control of a higher-level script or tool of some kind.
Perhaps there are compelling examples where this would not be the case, but I'm
not aware of them at the moment.

JK

A major use case could be for AucTeX preview of equations, or other wysywyg-like
interfaces where one wants to compile chunks of TeX code always with the same
preamble, and with no relevant changes in macros: one could have an ongoing TeX
run producing pdfs when provided with further input.

This raises the question of what state the TeX engine should return to when the hypothetical \nextpdf primitive is executed. Does it return to a pristine "initex" state, or a "freshly-loaded .fmt file" state, or is the current state completely unchanged (does \jobname reflect the new output name?), or what? Should the \count variables that are by convention used to record page numbers get reset?

Does a new .log file also get started? What about \write output files -- are they flushed and new files started?

There’s currently a thread called “startup time” about \dump’ing a new format file.
Similar kinds of consideration exist there, but at a different level (of course),
in choosing the best place to make that  \dump  call.

At least there it is clear what is the purpose for making the new format.
It is much less clear here what would be the new use-cases made possible
if such a  \nextpdf  primitive were made available.

  A currently-working
variant of this is the following (in bash), which ships out a first page, then
waits 10 seconds, then ships out another one.

$ (echo '\relax Hello world!\vfill\break' && sleep 10 && echo '\relax Another
pdf.\bye') | xetex

One could imagine a primitive \nextpdf that would make xetex produce 2 separate
pdfs (in the present case texput.pdf and secondfile.pdf)

$ (echo '\relax Hello world!\nextpdf{secondfile}' && sleep 10 && echo '\relax
Another pdf.\bye') | xetex

This looks equivalent to (xetex '\relax Hello world!\bye' && sleep 10 && xetex --jobname secondfile '\relax Another pdf.\bye'), right?

It's true there would be a difference if there are macros etc. defined while processing the first file, and then used while generating the second. But I'm not sure this is really a commonly-required use case.

Consider me not yet persuaded……

I’m on the fence too.

Of course another possibility for Phil is to put all the pages of *both* his desired PDFs into the same “master PDF”,
then use a command-line tool like  pdftk  to extract the relevant pages for one or other into a new PDF.

This would likely not work with Tagged PDF documents.
There the extraction into separate files would need to be done by Acrobat Pro,
so as to preserve the tagging structures and the page-based relationships of marked content.
But that’s an issue for the future.


JK



All the best.
Stay safe.

Ross


Dr Ross Moore
Department of Mathematics and Statistics
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