I am having a difficult time converting a list to "string"-- my real goal is to a number.

I have a list of 1 and 0s. An example is (1 0 1).  This is a binary number not a base 10 number.

How do I get the list to the form of "#B101".  I have tried to place the "nth" element to a string.
4. Break [6]> (setf (aref s 0) (nth 0 x))

*** - SYSTEM::STORE: 0 does not fit into "     ", bad type

where x is ( 1 0 1)
and   s is string of length 5

I am not sure this will get me to my goal.  I have tried to "eval" a string without luck.
What is the trick to this?

10. Break [12]> (setf t1 "#b101")
10. Break [12]> t1
10. Break [12]> (eval t1)

Thanks in advance....

Randy Justice