[tex-k] Is there a way to find the error line?

Wolfgang Helbig helbig at mailbox.org
Mon Mar 22 13:14:01 CET 2021

Dear Yannis,

> thank you very much for your advice. I think the problem came form the 
> fact that some WEB units
> are procedures (and therefore need a semicolon at the end) and others 
> are just code fragments
> that TANGLE will place at a location where semicolon is not allowed.
The code fragments in a WEB never end with semicolon. But at the places 
where they are used, Knuth always writes a semicolon even if not needed, 
i. e. before 'end'. Tangle is not an excuse. But Weave is, because the 
empty statement changes dramatically the formatting.
> BTW a question: when adding features to existing TeX engines is it 
> better to break the changes
> into many WEB units, so that their documentation is easier to follow 
> or to keep the existing WEB
> units so that people can refer to them by using stable unit numbers?
I'd use stable unit numbers.
> For example, if I modify substantially §1015 which is the \patterns 
> scanner, shall I rather break my
> modifications into new units and call them inside §1015, or keep a 
> long §1015 so that what was
> previously §1016 keeps the same identifier?

I'd suggest to change module 1015. In TeX-FPC I put new staff in the 
last part, System Changes,  a procedure to load the editor for error 
recovery, a code fragment to install an interrupt handler, and the 
interrupt handler, which is a procedure. BTW, TeX-FPC contains a 
polytonic font.

> Yannis
>> Le 22 mars 2021 à 11:28, Wolfgang Helbig <helbig at mailbox.org 
>> <mailto:helbig at mailbox.org>> a écrit :
>> Dear Yannis,
>> in Pascal, the semicolon seperates two statements, whereas in ALGOL 
>> and C, the semicolon terminates a statement.
>> Or in Pascal, the semicolon is never part of a statement and in C it 
>> is always is part of a statement.
>> In Pascal, the empty string is a statement, called "empty statement". 
>> It does nothing.
>> So in parts of the program, where the syntax rules allow one or more 
>> statements, you can always put the semicolon without changing the 
>> meaning of the program.
>> But there are places, where only one statement is accepted, notably 
>> the 'then' part of an if statement: A semicolon after the statement 
>> in the 'then'-part ends the 'if'-statement, which is followed by the 
>> empty statement. If your if-statement does have an else part, an 
>> 'else' is following the empty statement. But 'else' may only follow 
>> the 'then' part of the 'if'-statement, not the if-statement as a whole.
>> Unfortunately, some people misuse the empty statement and feel 
>> licensed to terminate every statement with a semicolon -- A confusing 
>> step backward in the evolution of ALGOL-like languages. A step 
>> forward of course is Dijkstra's Guarded Commands notation. In fact, 
>> the empty statement is the very first statement in Dijkstra: "A 
>> Discipline of Programming", 1976, p. 25. and in Jensen, Wirth: 
>> "Pascal User Manual and Report", 3rd ed. 1985, p. 169.
>> Alas, compilers are rare for dot.not, as I prefer to call Dijkstra's 
>> notation. You recognize by its dots in the notation for arrays.
>> greetings,
>> Wolfgang
>>> dear Karl,
>>> thanks for your answer. I finally found the error, it was an 
>>> unnecessary semicolon after an "end".
>>> I have a hard time finding the precise rules: when are semicolons 
>>> after "end" necessary / optional / forbidden?
>>> (The only thing I know for sure is that the semicolon is forbidden 
>>> when we are in an if-test
>>> and an "else" is following:
>>> if xxx begin xxx end else begin xxx end;   <--- no semicolon between 
>>> "end" and "else"
>>> but beside that I couldn't find precise information and TeX's Pascal 
>>> code is either not very consistent
>>> with respect to semicolons or maybe it follows some pattern that I 
>>> wasn't able to find out yet…)
>>> Thanks again for your help,
>>> Yannis
>>>> Le 21 mars 2021 à 02:57, Karl Berry <karl at freefriends.org 
>>>> <mailto:karl at freefriends.org>> a écrit :
>>>>    Is there a way to localize the error?
>>>> For the record, this is the brief reply I sent to when Yannis asked me
>>>> separately. It's all I have. Web2c is a lousy development environment,
>>>> no question.
>>>> -----------------------------------------------------------------------------
>>>> Date: Fri, 19 Mar 2021 11:19:09 -0700
>>>> From: Karl Berry <karl at freefriends.org <mailto:karl at freefriends.org>>
>>>> To: yannis1962 at gmail.com <mailto:yannis1962 at gmail.com>
>>>> Subject: Re: Debugging
>>>> In-Reply-To: <466F362F-4E43-4655-B0FC-2710ABD215AD at gmail.com 
>>>> <mailto:466F362F-4E43-4655-B0FC-2710ABD215AD at gmail.com>>
>>>>    Can you tell me how to localize the error?
>>>> There is no good way. Just have to go back to the original, make 
>>>> sure it
>>>> works, and add individual lines until you find the error, which
>>>> apparently has something to do with "true" and a semicolon.
>>>> Sometimes the .c file(s) left in (in your case)
>>>>  /var/folders/1n/fvs3dd2d5gqghwcw8khb41_h0000gn/T/
>>>> as given by the error msg provide a clue. [...]
>>> IMT Atlantique <http://www.imt-atlantique.fr/> 	
>>> *Yannis HARALAMBOUS*
>>> Professor
>>> Computer Science Department
>>> UMR CNRS 6285 Lab-STICC
>>> Site web IMT Atlantique 
>>> <http://perso.telecom-bretagne.eu/yannisharalambous/>Twitter IMT 
>>> Atlantique <https://twitter.com/y_haralambous>LinkedIn IMT 
>>> Atlantique 
>>> <https://www.linkedin.com/in/yannis-haralambous-5529073?trk=hp-identity-name>
>>> Technopôle Brest-Iroise CS 83818
>>> 29238 Brest Cedex 3, France
>>> Une école del'IMT <http://www.imt.fr/>
>>> /Any sufficiently advanced bug is indistinguishable from a 
>>> feature./     (Rich Kulawiec)
>> -- 
>> Wolfgang Helbig
>> Stauferstr. 22
>> 71334 Waiblingen
>> 07151-920 227
>> <helbig.vcf>
> IMT Atlantique <http://www.imt-atlantique.fr> 	
> Professor
> Computer Science Department
> Site web IMT Atlantique 
> <http://perso.telecom-bretagne.eu/yannisharalambous/>Twitter IMT 
> Atlantique <https://twitter.com/y_haralambous>LinkedIn IMT Atlantique 
> <https://www.linkedin.com/in/yannis-haralambous-5529073?trk=hp-identity-name>
> Technopôle Brest-Iroise CS 83818
> 29238 Brest Cedex 3, France
> Une école del'IMT <http://www.imt.fr>
> /Le lecteur a le droit et même parfois le devoir de savoir en quels 
> caractères
> est composé le livre qu'il a entre les mains, et on ne peut exiger de lui
> qu'il sache le reconnaître tout seul./  (Gérard Genette)

Wolfgang Helbig
Stauferstr. 22
71334 Waiblingen
07151-920 227

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