Common Lisp declarations are hints to the compiler that is doesn't have to do as much type checking, and so it can speed things up by omitting type checks, beca

Common Lisp declarations are hints to the compiler that is doesn't have to do as much type checking, and so it can speed things up by omitting type checks, because you the user told the compiler it was safe to do so. http://stackoverflow.com/a/12677731 http://stackoverflow.com/a/12677731 ...SBCL with certain level of safety declarations does mostly do what you really want though.