[NTG-context] Trying to understand this ctxlua error

[Gerben Wierda]

On 6 Apr 2020, at 02:54, Wolfgang Schuster <wolfgang.schuster.lists at gmail.com> wrote:
> 
> Gerben Wierda schrieb am 06.04.2020 um 00:41:
>> I got this error after I had changed some lua code:
>> tex error       > tex error on line 272 in file archimate-lua.new: ! Undefined control sequence
>>         warnIfVerbose( "Breaking off the processing of node %s\nNo
>>       l...eak                                                                     xsi:type", node)
>> \luat_start_lua_code_indeed ...ormalexpanded {\endgroup \noexpand \directlua {#1
>>                                                                                  }}
>> l.272 \stopluacode
>> <empty file>
>> The control sequence at the end of the top line of your error message was never
>> \def'ed. You can just continue as I'll forget about whatever was undefined.
>> I have been looking at that code for over two hours, not seeing anything wrong with it. But I’ve now finally found the culprit and I still do not get it.
>> The culprit was:
>>           warnIfVerbose( "Breaking off the processing of %s\n No elementRef", node)
>> The problem goes away when I use:
>>           warnIfVerbose( "Breaking off the processing of %s\nNo elementRef", node)
>> (I don’t want the line after the node is printed to begin with a space).
>> But the lack of space between \n and N kills lua (apparently). For completeness (as string.format and texio.write_nl are also in play):
>> function warnWithLabelIfVerbose( str, ... )
>>   if verboseProgram then
>>     texio.write_nl( str .. string.format(...))
>>   end
>> end
>> function warnIfVerbose( ... )
>>   warnWithLabelIfVerbose("-----> ", ...)
>> end
>> Is this a lua bug? A ConTeXt bug? Expected behaviour? And if so, why is reported that on line 272 (where \stopluacode is) is the error? Or is the error message indeed helpful and do I just lack the know how to interpret it?
> 
> ConTeXt expands TeX commands in a luacode-environment
> and when you have \n followed by text you create a new
> command with starts with \n but since it isn't defined
> you get a error message.
> 
> In the example below the commented block produces
> the same error message as you get.
> 
> \starttext
> 
> %\startluacode
> %print("text\ntext")
> %\stopluacode
> 
> \startluacode
> print("text\n text")
> \stopluacode
> 
> \stoptext

OK, thanks. This means the ConTeXt environment mixes standard TeX (where \nfoo would be considered a TeX command) and lua string substitution (where \nfoo would mean a newline followed by foo), correct? I understand why that happens (otherwise one would have to escape all \ characters directed at TeX) but it really took me hours (because I did not understand the error message that correctly told me \Nno was the problem). It’s what you see depends on what you are looking for, I guess.

Maybe a warning in the documentation (or maybe there is one and I missed it)

G

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