[NTG-context] How to extend an existing macro to take optional parameters?

[Bruce Horrocks]

> On 13 Mar 2023, at 21:39, Hans Hagen via ntg-context <ntg-context at ntg.nl> wrote:
> 
> On 3/12/2023 2:24 PM, Bruce Horrocks via ntg-context wrote:
>> I have an existing macro that I'd like to extend.
>> The current definition is \define[3]\mycommand{...} which I'd like to extend to take an optional 4th parameter plus an optional setup parameter.
>> Thus I currently invoke it as:
>>   \mycommand{aa}{bb}{cc}
>> and I'd like to be able to extend it so that any of the following can be used:
>>   \mycommand{aa}{bb}{cc}
>>   \mycommand{aa}{bb}{cc}{dd}
>>   \mycommand{aa}{bb}{cc}{dd}[ee]
>> or
>>   \mycommand[ee]{aa}{bb}{cc}{dd}  % if this is more the ConTeXt way
>> where {dd} is the optional extra parameter and, if it is present, then [ee] can also be optionally added (because it controls how {dd} is printed).
>> If it helps, the actual body of the macro can easily be a call to Lua so it's fine if the function takes 5 params where 4 and 5 can be nil or empty strings.
>> I've trawled through syst-aux.mkiv but it only covers optional numbers of [ ] or { } but not combinations of both (which given the vast numbers of combinations is perhaps not surprising!). Have I missed something obvious that would help me?
> So, four optional with mandate {} plus a fallback to an optional []
> 
> \starttext
> 
> \tolerant\def\mycommand#=#=#=#=#:[#5]%
>  {\ifparameter#1\or(1:#1)\fi
>   \ifparameter#2\or(2:#2)\fi
>   \ifparameter#3\or(3:#3)\fi
>   \ifparameter#4\or(4:#4)\fi
>   \ifparameter#5\or[5:#5]\fi}
> 
> \startbuffer
> \mycommand{aa}{bb}{cc}
>  \mycommand{aa}{bb}{cc}{dd}
>  \mycommand{aa}{bb}{cc}{dd}[ee]
> \mycommand{aa}{bb}{cc}
>  \mycommand{aa}{bb}{cc}{dd}
>  \mycommand{aa}{bb}{cc}{dd}[ee]
> \stopbuffer
> 
> \typebuffer
> 
> \startlines \getbuffer \stoplines
> 
> \stoptext
> 
> I'm not saying that it's the best solution, you can add \protected in front of the \def if needed.
> 
> Hans

Thanks Hans,

This works well. I'll try and add something to the Wiki but I don't understand how #: does what it does.

Regards,
—
Bruce Horrocks
Hampshire, UK