Chapter 41

struct.ss: Structure Utilities

To load: (require (lib "struct.ss"))

(copy-struct struct-id struct-expr (accessor-id field-expr) ···)      SYNTAX

This form provides ``functional update'' for structure instances. The result of evaluating struct-expr must be an instance of the structure type named by struct-id. The result of the copy-struct expression is a fresh instance of struct-id with the same field values as the result of struct-expr, except that the value for the field accessed by each accessor-id is replaced by the result of field-expr.

The result of struct-expr might be an instance of a sub-type of struct-id, but the result of the copy-struct expression is an immediate instance of struct-id. If struct-expr does not produce an instance of struct-id, the exn:fail:contract exception is raised.

If any accessor-id is not bound to an accessor of struct-id (according to the expansion-time information associated with struct-id), or if the same accessor-id is used twice, then a syntax error is raised.

(define-struct/properties id (field-id ···) ((prop-expr val-expr) ···) [inspector-expr])      SYNTAX

Like define-struct, but properties (see section 4.3 in PLT MzScheme: Language Manual) can be attached to the structure type. Each prop-expr should produce a structure-type property value, and each val-expr produces the corresponding value for the property.

Example:

(define-struct/properties point (x y) 
   ([prop:custom-write (lambda (p port write?)
                        (fprintf port "(~a, ~a)"
                                      (point-x p)
                                      (point-y p)))]))

(display (make-point 1 2)) ; prints (1, 2)

(make-->vector struct-id)      SYNTAX

This form builds a function that accepts a struct instance (matching struct-id) and provides a vector of the fields of the struct.