That lets you write c[ad]{1,10}r, or c[ad]{1,n}r with O(2^n) initialisation time. OP wanted to be able to write c[ad]+r. Also, that eval could be replaced with

That lets you write c[ad]{1,10}r, or c[ad]{1,n}r with O(2^n) initialisation time. OP wanted to be able to write c[ad]+r. Also, that eval could be replaced with (untested) (intern *ns* (symbol (str "c" name)) fun)