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Message-ID:  <CANQYN6zipdw0nkEB+ki2oJxG8o3N_YWsizzFKXxC89XpqcpFTA@mail.gmail.com>
Date:         Tue, 19 Aug 2014 21:58:28 +0200
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From: Bruno Le Floch <blflatex@GMAIL.COM>
Subject: Re: \directlua in LaTeX3
To: LATEX-L@LISTSERV.UNI-HEIDELBERG.DE
In-Reply-To:  <53F3931A.4080203@arcor.de>
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Envelope-To: <rainer.schoepf@GMX.NET>
Status: R

On 8/19/14, Stephan Hennig <mailing_list@arcor.de> wrote:
> Am 19.08.2014 um 19:21 schrieb Heiko Oberdiek:
>
>>> \ExplSyntaxOn
>>> \directlua{
>>>   local myarg = '\mymacro'
>>>   texio.write_nl('l3: argument is ' .. tostring(myarg))
>>> }
>>> [...]
>>> First, spaces are gone in Lua code.  Though, spaces are significant in
>>> Lua.
>>
>> `\ExplSyntaxOn' says that spaces are gone, that's the purpose of this
>> command. Explicit spaces are available via `~':
>
> Have already seen that when using l3's message mechanism, but didn't try
> in \directlua.  Thanks!
>
>
>>> Second, variable myarg is nil with \ExplSyntaxOn.  (I don't understand
>>> why.)
>>
>> Without spaces you get:
>>
>>   localmyarg='\mymacro'
>
> Should have seen that by myself.  Thanks again!
>
>
>> BTW, this is quite a risky way to pass the contents of user variables ot
>> Lua code. Consider syntax errors, if "\mymacro" contains ', or
>> "\mymacro" could even contain containing something like:
>>    '; very evil code; local dummy='
>>
>> There is \luaescapestring/\luatexluaescapestring:
>>
>>   '\luatexluaescapestring{\mymacro}'
>
> It's actually a language string that I'm evaluating to a number via
>
>   \the\csname l@#1\endcsname       or
>   \int_use:N\cs:w l@#1\cs_end:     in LaTeX3
>
> If #1 contains no valid language identifier, the expression should throw
> an error.  So, I think I'm safe here.  I'm indeed using \luaescapestring
> in other circumstances.
>
> Thanks!
> Stephan Hennig

Avoid using \cs:w ... \cs_end: constructions.  It is much better to
use a c-type argument, so for your case, \int_use:c { l@#1 }.

Regards,
Bruno