Common Lisp with SBCL: (defun double (x) (+ x x)) ; BigInts (or floats, for that matter) (defun double (x) (declare (type fixnum x)) (+ x

Common Lisp with SBCL: (defun double (x) (+ x x)) ; BigInts (or floats, for that matter) (defun double (x) (declare (type fixnum x)) (+ x x)) ; will emit an error if X is more than a long (defun double (x) (declare (type fixnum x) (optimize speed (safety 0))) (the fixnum (+ x x))) ; trusts that everything is a long - basically like C