[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 17:29:
> Dear list,
> 
> I have the following sample:
> 
>    \starttext
>    \def\MyCommand{\doquadruplegroupempty\doMyCommand}
> 
>    \def\doMyCommand#1#2#3#4{%
>      \iffourthargument
>        #4%
>      \orelse\ifthirdargument
>        #3%
>      \else
>        #2%
>      \fi}
> 
>    \MyCommand{}{second}{third}{fourth},\\
>    \MyCommand{}{second}{third}{fourth} e,\\
> 
>    \MyCommand{}{second}{third},\\
>    \MyCommand{}{second}{third} e,\\
> 
>    \MyCommand{}{second},\\
>    \MyCommand{}{second} e,\\
>    \stoptext
> 
> I don‘t know why only the command gets the space after right only when
> the four arguments are provided.
> 
> 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.

%%%% begin example
\tolerant\def\CommandA#_#*#_#*#_#*#_{(#1)(#2)(#3)(#4)}
\tolerant\def\CommandB#_#,#_#,#_#,#_{(#1)(#2)(#3)(#4)}
	
\starttext

A: \CommandA{a}          xxx\par
B: \CommandB{a}          xxx\blank

A: \CommandA{a}{b}       xxx\par
B: \CommandB{a}{b}       xxx\blank

A: \CommandA{a}{b}{c}    xxx\par
B: \CommandB{a}{b}{c}    xxx\blank

A: \CommandA{a}{b}{c}{d} xxx\par
B: \CommandB{a}{b}{c}{d} xxx\blank

\stoptext
%%%% end example

Another way to avoid this is to create a command with a key-value list.

%%%% begin example
\tolerant\def\Command[#1]%
   {\begingroup
    \getdummyparameters[#1]%
    \doifsomething{\dummyparameter{a}}{(\dummyparameter{a})}%
    \doifsomething{\dummyparameter{b}}{(\dummyparameter{b})}%
    \doifsomething{\dummyparameter{c}}{(\dummyparameter{c})}%
    \doifsomething{\dummyparameter{d}}{(\dummyparameter{d})}%
    \endgroup}

\starttext

\Command[a=1,b=2,c=3,d=4] xxx\par
\Command[a=1,c=3] xxx\par

\stoptext
%%%% end example
Wolfgang
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