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

Yannis Haralambous yannis1962 at gmail.com
Mon Mar 22 12:04:28 CET 2021

dear Wolfgang and others,

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.

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?

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?

eTeX's <Hyphenation codes for current language> has been placed at the end of the file, §1666, this
allows keeping numbers §1014, §1015, etc. unchanged, but makes it more difficult to read the code:
I have to permanently switch from PDF page 663 to PDF page 440…



> Le 22 mars 2021 à 11:28, Wolfgang Helbig <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. [...]
>>  <http://www.imt-atlantique.fr/>	Yannis HARALAMBOUS
>> Professor
>> Computer Science Department
>> UMR CNRS 6285 Lab-STICC
>>  <http://perso.telecom-bretagne.eu/yannisharalambous/> <https://twitter.com/y_haralambous> <https://www.linkedin.com/in/yannis-haralambous-5529073?trk=hp-identity-name>Technopôle Brest-Iroise CS 83818
>> 29238 Brest Cedex 3, France
>> Une école de l'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>

 <http://www.imt-atlantique.fr/>	Yannis HARALAMBOUS
Computer Science Department
 <http://perso.telecom-bretagne.eu/yannisharalambous/> <https://twitter.com/y_haralambous> <https://www.linkedin.com/in/yannis-haralambous-5529073?trk=hp-identity-name>Technopôle Brest-Iroise CS 83818
29238 Brest Cedex 3, France
Une école de l'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)

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