[tex-k] potential errata in The TeXbook and TeX: The Program, Jubilee editions

[eranyarkon at gmail.com]

Hi Karl,

Thanks so much for the follow up!

Eran

On Tue, Oct 31, 2023 at 12:48 PM Karl Berry <karl at freefriends.org> wrote:

> Hi Eran - back on your report from August 2022 (sorry).
>
>     *page 297:* The index for "remainder" should link to section 104
>     ("remainder, scaled") instead of 543 (different "remainder" from
>     font-metric file)
>
> Agreed. Added at
> https://tug.org/texmfbug/newbug.html#B297remainder.
>
>     *page 470, section 1127:* First line of align_error - should it
>     check for abs(align_state) > 1 instead of > 2? Since I assume you
>     want align_state to become zero by adding a single open or close
>     brace. I'm probably wrong.
>
> Here is DRF's analysis, concluding that no change is warranted. The fact
> that it's in the trip test is pretty persuasive.
>
> Let me know if questions/problems/changes ... --thanks, karl.
>
>
> Date: Mon, 16 Oct 2023 20:36:49 +0000 (UTC)
> From: David Fuchs
> To: Karl Berry
> Subject: B470: align_state
>
> OK, I'm going to go a little out on a limb on the align_state business,
> but I don't have high confidence level. Consider a basic alignment:
>
> \halign{\indent#\hfil&\hskip 1em#\hfil\cr
> A&B\cr
> CC&dd\cr
> EEEE&F\cr}
>
> Works fine.  Now, let's trigger align_error by changing "CC" to "C{C"
> which results in the expected "Missing } inserted" when TeX gets to the
> & (and then recovers OK with the default fix).  Good.  Now let's change
> to "C{{C" which gives a similar result, except that we get the "Missing
> } inserted" error twice, as you would expect.  Also good.
>
> But when we change to "C{{{C" we instead get the "Misplaced alignment
> tab character &" error message.
>
> My best guess is that the idea was that if you left out a closing brace
> by accident (so align_state is 1), or mis-typed a closing brace as an
> opening brace (so align_state is 2), it was deemed to be most likely
> that you had a simple case of messed up braces, and deserved a message
> that points in that direction.
>
> But if you're deeper than that into levels of unclosed left braces,
> something way worse might well be going on, and the warning should be
> more along the lines of indicating that you're deep in the weeds and not
> anywhere near an alignment (maybe you thought you were even out of
> it). And in such a situation, if you only got a zillion "Missing }
> inserted" messages, you may not quite have enough clues that it's due to
> alignment stuff (even though the Help text helps), and the more direct
> "Misplaced alignment tab character &" is more to the point.
>
> So, I don't know if that's the actual motivation for the test to be
> ">2" and maybe there's a better explanation.  Somehow I don't think is a
> mistake, though; the trip test does hit it.  -drf
>
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