Common Lisp supports arbitrary type predicates, and I think that SBCL enforces them (not sure) at runtime. For instance, it will call the predicate before setti

Common Lisp supports arbitrary type predicates, and I think that SBCL enforces them (not sure) at runtime. For instance, it will call the predicate before setting a struct's field to make sure that it returns true (under high safety compilation, low safety just trusts that it's correct)