I have written a polynomial class along the lines described in SICP 2.5.3 (except using defclass). I would like to be able to seamlessly add and multiply polynomials and regular numbers but I can't make change-class accept a number.

I tried to simplify the problem by changing class from an integer to a float:

(change-class 4 'float)

but that gave me the error:

There is no applicable method for the generic function
#<STANDARD-GENERIC-FUNCTION CHANGE-CLASS (7)>
when called with arguments
(4 #<BUILT-IN-CLASS FLOAT>).
[Condition of type SIMPLE-ERROR]

I get an error of the same form from (fyi):

(change-class 4 'polynomial)

I'm going to go ahead and implement a manual conversion but I would prefer to use the built-in clos facilities.