Utilities

Structure values can only be created and updated with the constructor and setter procedures created by define-struct, but structure values are not opaque. These utility functions work on with all structure values:

•   (struct? v) returns #t if v was created by any make-s or #f otherwise. All other built-in predicates return #f for values constructed by a make-s.
•   (struct-length v) returns the number of fields in the structure value v.
•   (struct-ref v n) returns the value of the nth field of the structure value v. (The first field is index 0.) If v does not have an nth field, the  exn:application:range:struct exception is raised.
•   (struct->vector v) converts the structure value v to a vector. The first slot of the result vector contains an identifier of the form struct:s. The remaining slots contain the values of the fields of v. The struct->vector procedure is intended for printing and debugging use.

The  struct-type? predicate returns #t if its argument is a structure type value or #f otherwise.

The  struct-setter-procedure? predicate returns #t if its argument is a setter procedure generated by define-struct or #f otherwise.

Two structure values are  eqv? if and only if they are  eq?. Two structure values are  equal? if they have the same structure type and their corresponding fields are all equal?.