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?
>
> Regards,
> Gerard
>
>
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