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

[Hans Hagen]

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

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                                           Hans Hagen | PRAGMA ADE
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