processaction in keyval lists

[Thomas A.Schmitz <thomas.schmitz@uni-bonn.de>]

All,

I couldn't resist spending some time today working on the Greek  
problem. I'm trying to write a proper module that would allow me to set  
up definitions for fonts and scaling. But I'm running into a problem   
that is beyond my meagre TeX abilities. I want to define the  
setup-command like so (using code that Taco send to the list a couple  
of months ago and that can be found on the wiki):

\unprotect

\def\setupgreek{\dodoubleempty\dosetupgreek}

\def\dosetupgreek#1[#2]{%
   \getparameters[GG][Scale=,Font=,#2]%Font,Scale
\edef\MyScale{\GGScale}%
\expandafter\processaction\expandafter[\GGFont]
    [SomeFont1     =>\def\MyFont{somefont },
     SomeFont2     =>\def\MyFont{someotherfont }]
}

\protect

\definebodyfont[4pt,5pt,6pt,7pt,8pt,9pt,10pt,10.5pt,11pt,12pt,14pt,14.4p 
t,16pt,18pt,20pt,22pt][rm][Gf=\MyFont sa \MyScale]

So I want this setup
\setupgreek[Scale=1.5,Font=SomeFont1]
to be expanded to somefont scaled at 1.5.

However, when I process a file, I always get this error:

! Undefined control sequence.
<argument> \MyFont
                    sa \MyScale
\parsefontspec #1->\xdef \somefontspec {#1
                                           \space }\@EA \doparsefontspec  
\som...

\xxdododefinefont ...tsize {#2}\parsefontspec {#4}
                                                   \newfontidentifier  
\let \l...

\fontstrategy ...ame #1\csname #2#3#4#5\endcsname
                                                   \tryingfontfalse \fi
<inserted text> ...yle \fontalternative \fontsize
                                                   \fi \iftryingfont  
\fontstr...

\synchronizefont ...strategy \the \fontstrategies
                                                   \relax \fi  
\ifskipfontchar...
...

When I add this line

\def\MyFont{somefont }

to the module, files compile without problems. So I conclude: the  
mistake is not in the definiton of MyFont itself, but my values are not  
getting processed the proper way; something in the \processaction part  
must be wrong. But I'm "stymied" here. Any suggestions would be most  
welcome!

Best

Thomas