Well, maybe "reject" was too strong a word. The warnings that are emitted by SBCL (Lisp implementation) are produced when two types don't intersect at all, som

Well, maybe "reject" was too strong a word. The warnings that are emitted by SBCL (Lisp implementation) are produced when two types don't intersect at all, something like "len(3)". There is no warning when types overlap. And even if the warning is issued, the code is still compiled and can run.