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define-struct/ properties

 (require mzlib/struct)

(copy-struct struct-id struct-expr
             (accessor-id field-expr) ...)
“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) ...)
maybe-inspector-expr = 
  | expr
Like define-struct from mzscheme, but properties 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.


> (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))

(1, 2)

(make-->vector struct-id)
Builds a function that accepts a structure type instance (matching struct-id) and provides a vector of the fields of the structure type instance.