[NTG-context] Re: wrong spacing after command with optional arguments

[Wolfgang Schuster <wolfgang.schuster.lists@gmail.com>]

Pablo Rodriguez via ntg-context schrieb am 26.04.2024 um 19:04:
> On 4/26/24 18:18, Wolfgang Schuster wrote:
>> Pablo Rodriguez via ntg-context schrieb am 26.04.2024 um 17:29:
>>> What is wrong in my definition above?
>>
>> There is nothing wrong, this is just a side effect of the scanner used
>> with the \do...groupempty commands. To have more control about this
>> behavior use the \tolerant modifier for \def to change it.
> 
> Many thanks for your reply, Wolfgang.
> 
> I tried this approach (I hope it isn’t wrong):
> 
>    \starttext
>    \expanded\tolerant\def\MyCommand#_#,#_#,#_#,#_{%
>      \doiftextelse{#4}%
>        {#4}
>        {\doiftextelse{#3}
>          {#3}
>          {#2}}}

The \expanded modifier is wrong (I guess you meant \unexpanded) but 
which check for the number of arguments you use doesn't matter in a 
document.

The LMTX version of the \iffourthargument etc. checks is the 
\ifarguments commands where you use \or to set a case for the number of 
argument passed.

\protected\tolerant\def\MyCommand#_#,#_#,#_#,#_%
   {\ifarguments
      % no arguments are passed
    \or
      #1% one argument is passed
    \or
      #2% two arguments are passed
    \or
      #3% three arguments are passed
    \or
      #4% four arguments are passed
    \fi}


>    \MyCommand{}{second}{third}{fourth},\\
>    \MyCommand{}{second}{third}{fourth} e,\\
> 
>    \MyCommand{}{second}{third},\\
>    \MyCommand{}{second}{third} e,\\
> 
>    \MyCommand{}{second},\\
>    \MyCommand{}{second} e,\\
>    \stoptext
> 
> BTW, this is the first time I see #_ instead of #1.
> 
> There is no way to search for "#_" in the wiki.
> 
> Grepping the source, "#_" seems to be used for optional arguments
> (mainly in syst-aux.mkxl).
> 
> But what are these "#_" (which don’t seem to come from TeX)?

Hans added many additions to command parameters in Luametatex and #_ 
means the argument to a commands has to be enclosed in braces while #1
allows you to pass text without it.

In the following example \CommandA take in the first case "a" as 
argument while CommandB ignores it and would only accept "{a}" with 
braces around it.

%%%% begin example
          \def\CommandA#1{(#1)}
\tolerant\def\CommandB#_{(#1)}

\starttext

\CommandA abc\par
\CommandB abc\blank

\CommandA {ab}c\par
\CommandB {ab}c\blank

\stoptext
%%%% end example

You can find a list with all new command parameters in lowlevel-macros.pdf.

Wolfgang
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