8.16.0.4
20 Compile-time Struct Info
| (require scramble/struct-info) | package: scramble-lib |
procedure
(adjust-struct-info base-info [ #:constructor constructor-id #:match-expander match-expander]) → struct-info? base-info : struct-info? constructor-id : (or/c identifier? #f) = #f match-expander : (or/c #f (-> syntax? syntax?)) = #f
Produces a struct-info record like base-info but with new behavior as a
constructor and match pattern. That is, if name is bound to the result
using define-syntax etc, and if constructor-id is not
#f, then a use of name as an expression is redirected to
constructor-id; and if match-expander is not #f, then
a use of name in a match pattern is expanded using
match-expander.
If base-info is an instance of a struct type with any of the following properties, the result has the same properties with the same values: prop:struct-auto-info, prop:struct-field-info. Other properties of base-info are not preserved.
The following example defines a point struct and then replaces
point with an adjusted struct info record that adds a contract and
makes one of the constructor arguments optional:
> (module point racket/base (provide (struct-out point)) (struct point (x y) #:transparent))
> (module point-adjusted racket/base (require (for-syntax racket/base scramble/struct-info) racket/contract (rename-in 'point [point orig-point])) (define (make-point x [y 0]) (orig-point x y)) (define-module-boundary-contract checked-make-point make-point (->* [real?] [real?] point?) #:name-for-blame point) (define-syntax point (adjust-struct-info (syntax-local-value #'orig-point) #:constructor #'checked-make-point)) (provide (struct-out point))) > (require 'point-adjusted) > (point 1 2) (point 1 2)
> (point 3) (point 3 0)
> (point 'hello 'goodbye) point: contract violation
expected: real?
given: 'hello
in: the 1st argument of
(->* (real?) (real?) point?)
contract from: 'point-adjusted
blaming: top-level
(assuming the contract is correct)
at: eval:2:0
> (struct point3 point (z) #:transparent) > (point3 1 2 3) (point3 1 2 3)