Common Lisp the Language
2nd Edition
If a type specifier is a list the car of the list is a symbol and the rest of the list is subsidiary type information. In many cases a subsidiary item may be unspecified. The unspecified subsidiary item is indicated by writing *. For example to completely specify a vector type one must mention the type of the elements and the length of the vector as for example
(vector double-float 100)
To leave the length unspecified one would write
(vector double-float *)
To leave the element type unspecified one would write
(vector * 100)
One may also leave both length and element type unspecified:
(vector * *)
Suppose that two type specifiers are the same except that the first has a * where the second has a more explicit specification. Then the second denotes a subtype of the type denoted by the first.
As a convenience if a list has one or more unspecified items at the end such items may simply be dropped rather than writing an explicit * for each one. If dropping all occurrences of * results in a singleton list If dropping all occurrences of * results in a singleton listeach one.ols>ns/next_motif.gif">