In CL you can't declare, for example, a proper-list-of type, which is to say a type which accepts a second type and represents a proper list containing only members of that second type.

  (deftype Proper-List-Of (subtype)
    `(or Null
         (Cons ,subtype
               (Proper-List-Of ,subtype))))

Doesn't work (for example). There kind of are ways to work around it to some extent with satisfies and ad-hoc predicate generation, but Coalton is a true value add in that aspect.