How to Nest a Variable Within a Define?

If you look at line 6, you'll notice I am trying to nest $2 into ${Xn}... I am having nothing but headaches with this. Anyone have any insight as how to get this right?

!macro messagebox TITLE BODY B1 X1 B2 X2 B3 X3 B4 X4
  Pop $R9 # Clear the Stack...
  IfErrors 0 -1
  messagebox::show "" "${TITLE}" "" "${BODY}" "${B1}" "${B2}" "${B3}" "${B4}"
   Pop $1
    IntOp $2 $2 + 1
  StrCmp $1 $2 ${X$2} -1
!macroend 

Thank you!

I now know this is impossible. I was pointed to the fact that I was trying to insert a runtime into a compiletime command. Sorry for the post :P