Is it possible to call a Common Lisp function in iOS?
If so, is it possible create it in a dynamic library?
It depends on what you mean by calling a CL function, but most likely ECL will be your shortest path. Start here, as there is a patch for ECL to better accommodate iOS: http://funcall.posterous.com/tag/iphone
ECL generates C code, so you should be in safe territory with Apple's shifting policies.