First of all, . won’t work in standard Racket because . has a special
meaning (see
https://docs.racket-lang.org/reference/reader.html#%28part._parse-pair%29).
But yes, this is directly related to the discussion above because with the
field name information, you can write your own accessor.
#lang racket
(module submodule racket
(provide @)
(require syntax/parse/define)
(define (access e fld)
(match-define-values (info _) (struct-info e))
;; for now we hard code it; would be able to extract it from
struct-type-info in Racket 2
(define fields '(bar baz))
(match-define-values (name _ _ accessor _ _ _ _) (struct-type-info info))
(accessor e (index-of fields fld)))
(define-simple-macro (@ e:expr fld:id) (access e 'fld)))
(require 'submodule)
(struct foo (bar baz) #:transparent)
(define my-foo (foo 1 2))
(@ my-foo baz) ;=> 2
Note that your struct must not be opaque for this to work. Typed Racket
might have enough compile-time data to make this to work with opaque
structs, though.
But for now, https://docs.racket-lang.org/struct-define/index.html might be
a good workaround for your problem.
On Fri, Jun 14, 2019 at 3:37 PM Dmitry Pavlov <dpav...@iaaras.ru> wrote:
> Hello,
>
> While we are at it: is it theoretically possible in Racket or Typed Racket
> (or will be possible in Racket 2 or Typed Racket 2) to access struct fields
> without repeating the name of the struct type again?
>
> Like in C
>
> typedef struct
> {
> double x;
> double y;
> } VeryLongStructureName;
>
> VeryLongStructureName a;
>
> double z = a.x + a.y;
>
>
> The analogous Racket code for the last line would be
>
> (define z (+ very-long-structure-name-x a) (+ very-long-structure-name-y
> a))
>
> and I am wondering whether it can be shortened to something like (define z
> (+ (. x a) (. x b)))
>
> (I know that match can work with structs, but it is not always as
> convenient as the C way with the dot)
>
>
> Best regards,
>
> Dmitry
>
>
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