A symbol naming the new union type descriptor
A string specifying the foreign name of the type
A sequence of symbols, possibly with type descriptions, naming the slots of the union.
A symbol naming the slot.
The FLI type of the slot.
is used to define a FLI union type specifier, which corresponds to the C
type. It is a convenience function, as a union type could also be defined using define-foreign-type.
A union is an aggregate type, or collection, of other FLI types. The types contained in a union are referred to as slots, and can be accessed using the foreign-slot-type and foreign-slot-value functions.
LispWorks Foreign Language Interface User Guide and Reference Manual - 7 Dec 2011