Here are some of my latest (failed) experiments:
#lang racket
(require (for-syntax racket/struct-info))
(require racket/pretty)
(struct foo (a b) #:transparent)
(displayln `("a foo object is transparent: I can see inside: \n
(struct->vector (foo 1 2)) ~~> "
,(struct->vector (foo 1 2))))
(displayln `("syntax object is opaque I can't see inside: \n
(struct->vector #'foo) ~~> "
,(struct->vector #'foo)))
;;; Why do two copies of the syntax display? (One copy
;;; is a side-effect. The other is a result).
;;; At expansion time, I can get some graphics in Dr-Racket for
;;; definition of foo, but I cannot get likewise
;;; not into the definition of syntax.
(begin-for-syntax
(displayln
(extract-struct-info
(syntax-local-value
#'foo)))) ; #'syntax))))
;;; But the access procedures for #'syntax are known!?!? (I just
;;; happen to know that there is a procedure named 'syntax-position';
;;; my whole issue is in trying to find out the list of all
;;; procedures defined in the system when the syntax type is created!)
(syntax-position #'42)
;;; Whereas #'foo is known in this module scope,
;;; (syntax struct:foo) is not known! Looks like the shorthand
;;; #'whatever for making a syntax object is known, but the longhand,
;;; presumably (syntax 'whatever), is not known.
(begin-for-syntax
(displayln
(extract-struct-info
(syntax-local-value
#'syntax))))
~~~~~~~~
Welcome to DrRacket, version 8.2 [cs].
Language: racket, with debugging; memory limit: 128 MB.
(.#<syntax:GSI/nanosim-apu-docs/WIKIS/BELEX_3/racket-sandbx-public.rkt:6:8
struct:foo>
.#<syntax:GSI/nanosim-apu-docs/WIKIS/BELEX_3/racket-sandbx-public.rkt:6:8
foo>
.#<syntax:GSI/nanosim-apu-docs/WIKIS/BELEX_3/racket-sandbx-public.rkt:6:8
foo?>
(.#<syntax:GSI/nanosim-apu-docs/WIKIS/BELEX_3/racket-sandbx-public.rkt:6:8
foo-b>
.#<syntax:GSI/nanosim-apu-docs/WIKIS/BELEX_3/racket-sandbx-public.rkt:6:8
foo-a>) (#f #f) #t)
. .
../../../../../../usr/share/racket/pkgs/errortrace-lib/errortrace/stacktrace.rkt:690:2:
extract-struct-info: contract violation
expected: struct-info?
given: #<procedure:...rivate/template.rkt:563:0>
>
On Friday, October 29, 2021 at 4:10:37 PM UTC-7 Siddhartha Kasivajhula
wrote:
> I was able to find this interface
> <https://docs.racket-lang.org/reference/inspectors.html#%28def._%28%28quote._~23~25kernel%29._struct-type-info%29%29>,
>
> but it doesn't quite provide the same information. E.g. (struct-type-info
> struct:foo)
>
> The ability to "introspect" values in a shell (or in the application) is
> useful in languages like python (e.g. dir(object) tells you what methods
> it provides, help(anything) gives you the interface/function signature,
> docstrings, etc.). I haven't seen this style emphasized in Racket
> documentation, and that may be because racket isn't object-oriented by
> default as python is, so that there often isn't a single object
> encapsulating all of this information.
>
> But all the same, if there are analogous facilities in racket, like the
> kind Brian asked about, I'd love to know as well.
>
>
> On Fri, Oct 29, 2021 at 3:14 PM Brian Beckman <[email protected]> wrote:
>
>> Well, as I understand it, a struct (usually? always?), #:transparent or
>> not, when declared, defines symbols that are meant to be visible in the
>> current scope, so (struct foo (a b)) defines foo #|constructor|#, foo?
>> #|instance-predicate|# foo-a and foo-b #|data accessors|# , that I can call
>> on instances:
>>
>> (struct foo (a b))
>> (let ([my-foo (foo 42 37)]
>> (list (foo? my-foo)
>> (foo-a my-foo)
>> (foo-b my-foo))) ~~> '(#t 42 37)
>>
>> I would like, given only the symbol foo referring to the struct type
>> itself, to discover (at least) the list of procedures foo?, foo-a, foo-b,
>> plus anything else the author of foo (the type) wants me to see.
>>
>>
>> On Fri, Oct 29, 2021 at 1:45 PM John Clements <[email protected]>
>> wrote:
>>
>>> In the text below, you refer to the “public” interface. Can I ask what
>>> you mean by “public” in this context?
>>>
>>> John
>>>
>>> > On Oct 29, 2021, at 11:16 AM, Brian Beckman <[email protected]>
>>> wrote:
>>> >
>>> > I believe that run time will be the most plausible use case. I may
>>> write macros that refer to struct-procedure names at macro-writing time,
>>> but I don't expect to invoke the struct procedures at macro-expansion time.
>>> My primary issue is "discoverability:" how can I find out the interface of
>>> any struct?
>>> >
>>> > On Thursday, October 28, 2021 at 1:00:15 PM UTC-7 [email protected]
>>> wrote:
>>> > Are you intending to use the struct procedure names at compile time
>>> (such as in a macro) or runtime?
>>> >
>>> > On Tuesday, October 26, 2021 at 5:02:46 PM UTC-7 [email protected]
>>> wrote:
>>> > I understand why structs are opaque, by default, but I want to
>>> discover the public interface of some struct type, that is, a list of the
>>> procedures defined by the struct.
>>> >
>>> > Here is an example. Suppose I want to find out all the procedures
>>> defined on an instance of the syntax struct
>>> >
>>> > #'42
>>> >
>>> > Dr. Racket shows an expander clicky that shows some formatted
>>> information inside the instance :
>>> >
>>> >
>>> >
>>> > Uncapitializing the names in the display reveals the interface:
>>> >
>>> > (syntax-position #'42) ~~> 790
>>> > (syntax-span #'42) ~~> 2
>>> > (syntax-original? #'42) ~~> #t
>>> >
>>> > etc.
>>> >
>>> > I want to discover those procedure names in my racket program, not
>>> manually by visually inspecting graphics in Dr Racket.
>>> >
>>> > I found this trick for structs that I define:
>>> >
>>> > #lang racket
>>> > (require (for-syntax racket/struct-info))
>>> > (require racket/pretty)
>>> >
>>> > (struct foo (a b))
>>> > (begin-for-syntax
>>> > (displayln
>>> > (extract-struct-info
>>> > (syntax-local-value
>>> > #'foo))))
>>> >
>>> > ~~>
>>> >
>>> >
>>> >
>>> > but it doesn't work for the syntax type
>>> >
>>> > (begin-for-syntax
>>> > (displayln
>>> > (extract-struct-info
>>> > (syntax-local-value
>>> > #'syntax))))
>>> >
>>> > ~~>
>>> >
>>> >
>>> >
>>> > I'd be grateful for advice and an example of how to get the interface
>>> of "syntax" without Dr Racket and without grovelling docs.
>>> >
>>> > --
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>>> .
>>>
>>> --
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>>
> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/racket-users/CAK2VK6tMxFH0oEq4iCgk7PW-4yJTB8xNr_b3F6GPwQS1MZVLwQ%40mail.gmail.com
>>
>> <https://groups.google.com/d/msgid/racket-users/CAK2VK6tMxFH0oEq4iCgk7PW-4yJTB8xNr_b3F6GPwQS1MZVLwQ%40mail.gmail.com?utm_medium=email&utm_source=footer>
>> .
>>
>
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