Structure Utilities

Structures can only be created and changed with the constructor and setter procedures created by struct, but structures are not opaque. These utility procedures work with all structure instance 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 field values in the structure v.
• (struct-ref v n) returns the value of the nth field of the structure v. (The first field is index 0.) If v does not have an nth field value, 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 symbol of the form struct:s. The remaining slots contain the field values of v. The struct->vector procedure is intended for printing and debugging use.

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 field values are all equal?.

Each kind of value returned by struct has a recognizing predicate:

• (struct-type? v) returns #t if v is a structure type descriptor value, #f otherwise.
• (struct-constructor-procedure? v) returns #t if v is a constructor procedure generated by struct, #f otherwise.
• (struct-predicate-procedure? v) returns #t if v is a predicate procedure generated by struct, #f otherwise.
• (struct-selector-procedure? v) returns #t if v is a selector procedure generated by struct, #f otherwise.
• (struct-setter-procedure? v) returns #t if v is a setter procedure generated by struct, #f otherwise.