There is a terminology confusion in the PL world, and in a way Racket is well positioned to clarify these problems (except that people won't change their language).
Things that happen at run-time: (struct s (x y z)) is a structure type definition (s 1 2 3) is a structure instance s is the structure constructor (define a (s 1 2 3)) defines a name for a structure type instance (s? a) determines whether a is an instance of s (s-x a) tag checks a to make sure it's an instance of s and then retrieves the x field Things that happen at compile time: Integer is a type -> is a type constructor, it constructs a new type from two other types (so does Listof) (define-type-alias (Opt t) (U False t)) is a type alias definition, parameterized over t (Opt Integer) is a short-hand for (U False Integer), derived from a type alias definition I don't think we have type-alias definitions with keywords. But then again, I see no problem with this idea. I am not sure whether this answers Alexander's question but I thought I'd mention the above since it's a bit common to conflate these ideas. -- Matthias ____________________ Racket Users list: http://lists.racket-lang.org/users
