The reason I switched from Scheme to Common Lisp was because I could say... (defun foo (x) (declare (type (Integer 0 100) x)) (* x (get-some-v

The reason I switched from Scheme to Common Lisp was because I could say... (defun foo (x) (declare (type (Integer 0 100) x)) (* x (get-some-value-from-somewhere-else))) And then do a (describe 'foo) in the REPL to get Lisp to tell me that it wants an integer from 0 to 100.