[NTG-context] Struggling with startuseMPgraphic and string argument!

[Geert Verhaag]

On 18-09-2020 09:03, Hans Hagen wrote:
> On 9/17/2020 9:41 PM, Geert Verhaag wrote:
>> Hi ConTeXt users,
>>
>> That's indeed magic and it works! Hans, thanks for your prompt answer!
>>
>> But I would like to take this a step further, by introducing a macro 
>> within the start/stopuseMPgraphic structure like so:
>>
>> \startuseMPgraphic{name}{s::lbl}
>>    def mymacro (text lb) =
>>      pair a ; a := (3cm,3cm) ;label.top("String: " & str lb,a) ;
>>    enddef ;
>>    mymacro(\MPvariable{lbl}) ;
>> \stopuseMPgraphic
>>
>> and this works too, but what if I introduce another text argument like:
>>
>> \startuseMPgraphic{name}{s::lbl,s::label}
>>    def mymacro (text lb,lbx) =
>>      pair a ; a := (3cm,3cm) ;label.top("String: " & str lb & ", " & 
>> str lbx,a) ;
>>    enddef ;
>>    mymacro(\MPvariable{lbl},\MPvariable{label}) ;
>> \stopuseMPgraphic
>>
>> However this doesn't work!  It gives the following error:
>>
>> ! Missing argument to mymacro.
>>
>> Isn't that weird? But perhaps it has to do with me not understanding 
>> argument passing properly within METAPOST macros!
>>
>> Can someone please explain why this 2 argument example doesn't work?
>>
>> (But maybe this isn't the proper list to ask questions like these. If 
>> so, I'm sorry for bothering you!)
>>
>> Regards,
>> Gerard
>>
>>
>> On 16-09-2020 16:32, Geert Verhaag wrote:
>>>
>>> Hi,
>>>
>>> I'm trying to pass a string argument value to an MPgraphic but it 
>>> doesn't seem to work:
>>>
>>> Tried the following:
>>>
>>> \startuseMPgraphic{name}{lbl}
>>>   pair a ; a := (3cm,3cm) ;label.top("\MPvariable{lbl}",a) ;
>>> \stopuseMPgraphic
>>>
>>> \starttext
>>>   \useMPgraphic{name}{lbl=1}
>>> \stoptext
>>>
>>> The above works as expected!
>>>
>>> But the following doesn't:
>>>
>>> \startuseMPgraphic{name}{lbl}
>>>   pair a ; a := (3cm,3cm) ;label.top("\MPvariable{lbl}",a) ;
>>> \stopuseMPgraphic
>>>
>>> \starttext
>>>   \useMPgraphic{name}{lbl=abc}
>>> \stoptext
>>>
>>> It yields:
>>>
>>>  1 \startuseMPgraphic{name}{lbl}
>>>  2       pair a ; a := (3cm,3cm) ;label.top("\MPvariable{lbl}",a) ;
>>>  3     \stopuseMPgraphic
>>>  4
>>>  5     %\startuseMPgraphic{name}fill fullcircle scaled 200pt 
>>> withcolor .625yellow ;\stopuseMPgraphic
>>>  6
>>>  7     \starttext
>>>  8      Example:
>>>  9 >>    \useMPgraphic{name}{lbl=abc}
>>> 10     \stoptext
>>> 11
>>>
>>> <to be read again>
>>> a
>>> \m_meta_current_variable a-a
>>>                             bc
>>> <argument> ... \hbox {\scratchdimen \m_meta_current_variable
>>>                                                   sp}\ifzeropt \wd 
>>> \b_meta_v...
>>> \secondoftwoarguments #1#2b-#2
>>>
>>> \9>>1 #1,2-\meta_prepare_instance_variable {#1}
>>> \syst_helpers_do_process_comm...
>>> \syst_helpers_do_process_comma_list ...rgument #1,
>>>                                                   ]\relax \global 
>>> \advance \...
>>> ...
>>> l.9   \useMPgraphic{name}{lbl=abc}
>>>
>>> So it seems that only numbers can be passed not character strings! 
>>> Why is that? Is there a possibility to achieve this functionality?
> \startuseMPgraphic{name}{s::lbl,s::label}
>     def mymacro(expr a, b) =
>         label.top("str:(" & a & "," & b & ")",(3cm,3cm)) ;
>     enddef ;
>     mymacro("\MPvariable{lbl}","\MPvariable{label}")
> \stopuseMPgraphic
>
> \starttext
>   \useMPgraphic{name}{lbl=abc,label=pqr}
>   \useMPgraphic{name}{lbl=def,label=xyz}
> \stoptext
>
> -----------------------------------------------------------------
>                                           Hans Hagen | PRAGMA ADE
>               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
> -----------------------------------------------------------------

Hi Hans,

It really is in the details!!!

I was convinced that I did something wrong somewhere, but couldn't 
figure out what.

Thanks very much for your kind help!

Regards,
Gerard