Any way to avoid nested case statements for proc taking two variant objects?

[doofenstein]

writing a macro to perform this operation would really not be that hard (for 
reference, this is my macro: 
<https://gist.github.com/RSDuck/c66ca50f8cd5b7a6ff7b115f3e8114b7#file-instrdecoding-nim-L119>
 it does a bunch of other things related to instruction decoding as well). 
Though I agree that as long as performance isn't so important it's not worth 
it. In my case the cpu interpreter is the most intensively used part of most 
emulators, so I had a good reason to optimise this.