I'm trying to do something with ${eval} in Conky, but I'm having problems even with a minimal example:

${eval ${exec echo '${font DejaVu Sans Mono :size=6}hey!'}}

As far as I understand, I would believe that I should see the string "hey!" printed with the 'DejaVu Sans Mono' font, but instead I'm getting this as output:

${font DejaVu Sans Mono :size=6}hey!

I want to be able to execute something as I would in the terminal, and then parse that as a Conky statement. Isn't the whole idea of $eval to parse that string again? If so, am I doing something wrong, am I misunderstanding how it works, or is that a bug in $eval?