Re: [NTG-context] Defining command with optional and mandatory arguments

24 May 2018


      On 5/24/2018 11:21 AM, Christoph Reller wrote:
...
On Wed, 23 May 2018 16:01:05 +0200, Hans Hagen  wrote:
...
On 5/23/2018 3:39 PM, Christoph Reller wrote:
...
Hi,
What is the right way to define a command with both mandatory and
optional arguments, e.g:
\MyCommand[optional][mandatory]
Consider the following MWE:
\unexpanded\def\MyCommand[#1]{
    \dosingleempty{\doMyCommand[#1]}}
\def\doMyCommand[#1][#2]{
    \doifsomething{#1}{number 1: #1\par}
    \doifsomething{#2}{number 2: #2}\blank[big]}
\starttext
\MyCommand[A][B]
\MyCommand[A]
\stoptext
In last year's versions of ConTeXt the output was
number 1: A
number 2: B
number 1: A
In the latest version of ConTeXt the output is
number 1: A
number 2: B
number 2: A
Is this behavior intended? How can I make a definition whose behavior
does not change in new versions of ConTeXt?
i'm not sure wht happens at your end but this is the best way:
\unexpanded\def\MyCommand
    {\dodoubleempty\doMyCommand}
\def\doMyCommand[#1][#2]%
    {\iffirstargument
       number 1: #1%
       \par
     \fi
     \ifsecondargument
       number 2: #2%
     \fi
     \blank[big]}
\starttext
      \MyCommand[A][B]
      \MyCommand[A]
\stoptext
Thank you Hans for this information. My question is rather about error
handling. I want:
\MyCommand[A][B] % <- succeeds with #1->A, #2->B
\MyCommand[A] % <- succeeds with #1->A
\MyCommand % <- fails with "! Use of \MyCommand doesn't match its definition"
I just wanted to ask whether there is a standard way to achieve this
with \do<whatever>empty. If not, then this is also okay.
just use \dodoubleempty instead
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