Types may be either named or anonymous. With structure and union types, the name is part of the type specifier, allowing recursively defined types such as:
An anonymous structure or union type is specified by using the name nil. The with-alien (page(struct foo (a (* (struct foo))))
) macro defines a local scope which
``captures'' any named type definitions. Other types are not
inherently named, but can be given named abbreviations using
def-alien-type.
[Macro]
alien: def-alien-type name type
This macro globally defines name as a shorthand for the Alien type type. When introducing global structure and union type definitions, name may be nil, in which case the name to define is taken from the type's name.