Note that I wrote "optional static type checks".

CL is always strongly typed. A character array, for example, stays as a character array. It can't be used directly in place of a byte array, for example.

But what it allows, optionally, are type declarations. These, in implementations like SBCL, allow compile-time ("static") type checking.

The declarations also allow big enhancements in code speed, because this produces code that is specific to a data type (you can always see the compiled assembly code for a lisp function by using the "disassemble" function)