Minor bug in Lua or ConTeXt

Minor bug in Lua or ConTeXt

[Bruce Horrocks via ntg-context]

ConTeXt  ver: 2023.01.04

The following MWE won't compile because of the \dummycommand line even though it is a comment. Not sure whether it's a minor bug or an unavoidable aspect of allowing embedded Lua.

\startluacode
-- \dummycommand
\stopluacode
\starttext
Hello
\stoptext

—
Bruce Horrocks
Hampshire, UK

___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : https://contextgarden.net
___________________________________________________________________________________

Re: Minor bug in Lua or ConTeXt

[Pablo Rodriguez via ntg-context]

On 1/18/23 00:36, Bruce Horrocks via ntg-context wrote:
> ConTeXt  ver: 2023.01.04
> 
> The following MWE won't compile because of the \dummycommand line
> even though it is a comment. Not sure whether it's a minor bug or an
> unavoidable aspect of allowing embedded Lua.

Hi Bruce,

I think your code should read:

  \startluacode
  -- \\dummycommand
  \stopluacode
  \starttext
  Hello
  \stoptext

BTW, in pure Lua:

  a = "\a"
  b = "\\b"
  print(a..b)

outputs "\b".

Sorry, I lack the knowledge to explain this, but backslash seems to be
an special char in pure Lua too.

Just in case it might help,

Pablo
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : https://contextgarden.net
___________________________________________________________________________________

Re: Minor bug in Lua or ConTeXt

[Hans Hagen via ntg-context]

On 1/18/2023 12:36 AM, Bruce Horrocks via ntg-context wrote:
> ConTeXt  ver: 2023.01.04
> 
> The following MWE won't compile because of the \dummycommand line even though it is a comment. Not sure whether it's a minor bug or an unavoidable aspect of allowing embedded Lua.
> 
> \startluacode
> -- \dummycommand
> \stopluacode
> \starttext
> Hello
> \stoptext

a bang-head-against-the-wall case:

\let\dummycommand\relax

\startluacode
-- \dummycommand
\stopluacode
\starttext
Hello
\stoptext

or:

\ifdefined\dummycommand \else \let\dummycommand\relax \fi

a document-on-the-wiki challenge for Pablo

Hans

-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------

___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : https://contextgarden.net
___________________________________________________________________________________

Re: Minor bug in Lua or ConTeXt

[Bruce Horrocks via ntg-context]

Thanks Hans.

Before Pablo spends too much effort on the wiki it's worth pointing out that this only happened because I was in-line documenting the Lua function that I had written and wanted to name the ConTeXT macro that would invoke it - so it's trivial for me to avoid this error.

Perhaps the Wiki only needs to point out that if you get a Lua related error and the error log lists the entire contents of \startluacode ... \stopluacode then a possible source of the error is a \command somewhere in there?

Regards,


> On 18 Jan 2023, at 09:48, Hans Hagen via ntg-context <ntg-context@ntg.nl> wrote:
> 
> On 1/18/2023 12:36 AM, Bruce Horrocks via ntg-context wrote:
>> ConTeXt  ver: 2023.01.04
>> The following MWE won't compile because of the \dummycommand line even though it is a comment. Not sure whether it's a minor bug or an unavoidable aspect of allowing embedded Lua.
>> \startluacode
>> -- \dummycommand
>> \stopluacode
>> \starttext
>> Hello
>> \stoptext
> 
> a bang-head-against-the-wall case:
> 
> \let\dummycommand\relax
> 
> \startluacode
> -- \dummycommand
> \stopluacode
> \starttext
> Hello
> \stoptext
> 
> or:
> 
> \ifdefined\dummycommand \else \let\dummycommand\relax \fi
> 
> a document-on-the-wiki challenge for Pablo
> 
> Hans
> 
> -----------------------------------------------------------------
>                                          Hans Hagen | PRAGMA ADE
>              Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>       tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
> -----------------------------------------------------------------
> 
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to the Wiki!
> 
> maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
> archive  : https://bitbucket.org/phg/context-mirror/commits/
> wiki     : https://contextgarden.net
> ___________________________________________________________________________________

—
Bruce Horrocks
Hampshire, UK

___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : https://contextgarden.net
___________________________________________________________________________________

Re: Minor bug in Lua or ConTeXt

[Pablo Rodriguez via ntg-context]

On 1/18/23 14:41, Bruce Horrocks via ntg-context wrote:
> […] 
> Perhaps the Wiki only needs to point out that if you get a Lua
> related error and the error log lists the entire contents of \startluacode ...
> \stopluacode then a possible source of the error is a \command somewhere
> in there?

Hi Bruce,

from what I understand is that undefined TeX commands cannot be added to
Lua comments.

If I’m not wrong (in my previous statement), I think this is
counterintuitive, since undefined commands are fine in TeX comments and
undefined variables are fine inside \startluacode … \stopluacode.

So I added
https://wiki.contextgarden.net/Programming_in_LuaTeX#Undefined_Commands_in_Lua_Comments.

Let me know whether I missed something.

Many thanks for your help,

Pablo
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : https://contextgarden.net
___________________________________________________________________________________

Re: Minor bug in Lua or ConTeXt

[Hans Hagen via ntg-context]

On 1/18/2023 6:47 PM, Pablo Rodriguez via ntg-context wrote:

> from what I understand is that undefined TeX commands cannot be added to
> Lua comments.

Indeed. Of course we could have some 'ignore undefined command' feature 
but that cripples the engine as well as then also never gives warning in 
the case you *do* want to expand.

> If I’m not wrong (in my previous statement), I think this is
> counterintuitive, since undefined commands are fine in TeX comments and
> undefined variables are fine inside \startluacode … \stopluacode.
I bet you'd complain if \the\scratchdimen would not expand. You cannot 
expect context to completely parse what goes into lua beforehand, unless 
you are willing to get a performance hit (apart from a waste of time).

And even if we'd make e.g. - active (with some lookahead magick) and 
then gobble till the end of the line we would get questions why it 
doesn't work in macros.

It's a small price to pay. (I also bet that Bruce is willing to \relax 
the command.)

Thanks for adding to the wiki,

Hans

-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------

___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : https://contextgarden.net
___________________________________________________________________________________

Re: Minor bug in Lua or ConTeXt

[Pablo Rodriguez via ntg-context]

On 1/18/23 19:07, Hans Hagen via ntg-context wrote:
> On 1/18/2023 6:47 PM, Pablo Rodriguez via ntg-context wrote:
> [...] 
>> If I’m not wrong (in my previous statement), I think this is
>> counterintuitive, since undefined commands are fine in TeX comments and
>> undefined variables are fine inside \startluacode … \stopluacode.
>
> I bet you'd complain if \the\scratchdimen would not expand. You cannot 
> expect context to completely parse what goes into lua beforehand, unless 
> you are willing to get a performance hit (apart from a waste of time).

I’m starting to understand that one cannot have it all.

I haven’t used so much Lua code to add an undefined TeX command in a
comment.

Different reply isn’t wrong, only it needs to be known in advance.

> Thanks for adding to the wiki,

I have discovered after the addition that this was explained before
(last paragraph from
https://wiki.contextgarden.net/Programming_in_LuaTeX#Calling_Lua_from_TeX).

To emphasize it visually, I abused the <blockquote> element.

If any wiki wizard knows better, please tell.

Many thanks for your help,

Pablo

___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!

maillist : ntg-context@ntg.nl / https://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : https://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : https://contextgarden.net
___________________________________________________________________________________