Passing the value of one parameter to another

Quite a stupid Vim question, but I need to do something and I can't find a solution to help. So here goes ...

(this is just an example, I'm not necessarily only interested in guifont and printfont)

set guifont?

      

        
        
        
      

    

gives out ...

How can I tell

set printfont=guifont

      

        
        
        
      

    

i.e. pass the string you get from guifont?

to printfont

?