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

[Hans Hagen]

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

-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------