[NTG-context] Commands with arguments with MetaPost

[Troy Henderson]

I would like to be able to do something like this

\def\foo#1{
    \startMPcode
        fill (0,0)--(598,0)--(598,50)--(0,50)--cycle withcolor green;
        label.rt(btex #1 etex),(50,25);
  \stopMPcode
}

and then use this in my ConTeXt document by

\foo{Some text}

However, my syntax seems to be incorrect, and I would appreciate any
help in fixing it.

Thanks,

Troy Henderson