Hi Brian,
A few random thoughts:
> 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.
When you want to look this up, is it in the repl (i.e. at runtime)?
The standard `struct` construct doesn't store much reflection information.
Instead of fighting the standard construct, you can consider making a
little variation.
If you are satisfied with having info for the structs defined in your own
program
(i.e. modules you have written yourself), then you can consider making a
module, say, `fancy-struct` that exports a macro where
(fancy-struct yada ...)
expands into
(begin
(fancy-struct yada ...)
<store reflection information>)
Using `rename-out` you can export it as `struct`, so it can be used without
changing any existing code.
/Jens Axel
Den søn. 31. okt. 2021 kl. 11.42 skrev Matt Jadud <[email protected]>:
> Hi Brian,
>
> Does this help move you forward?
>
> It has been a while since I've stared at macros in Racket, so this might
> be easier...
>
> Also, make sure you're executing this code in a module. If you're working
> in a REPL, I suspect all bets are off. It is certainly the case that you
> could combine several of my exploration steps into a simpler/cleaner macro,
> instead of generating lists of symbols, converting them back to syntax
> objects, and so on.
>
> Also, as a solution/exploration, I... don't know how this would interact
> with the full range of possible structs. Someone who knows more about
> syntax and structs should be able to speak to how you'd find out all of the
> defined functions that spawn from struct definition/creation. (It might
> also be useful to know *why* you want to destructure structs this way?
> Knowing that may illuminate some other path forward.)
>
> #lang racket
> (require racket/struct-info)
>
> (struct A (b c))
>
> (struct B (e f) #:transparent)
>
> (require (for-syntax racket/struct-info))
> (define-syntax (get-field-names stx)
> (syntax-case stx ()
> [(_ sym)
> #`(quote
> #,(struct-field-info-list
> (syntax-local-value #'sym)))
> ]))
>
> ;; These let me see the field names
> (get-field-names A)
> ;; Returns '(c b)
> (get-field-names B)
> ;; Returns '(f e)
>
> ;;
> https://stackoverflow.com/questions/20076868/how-to-know-whether-a-racket-variable-is-defined-or-not
> (define-syntax (defined? stx)
> (syntax-case stx ()
> [(_ id)
> (with-syntax ([v (identifier-binding #'id)])
> #''v)]))
>
> (define-syntax (proc-names stx)
> (syntax-case stx ()
> [(_ sym)
> (let ([names (map (λ (s)
> (string->symbol
> (format "~a-~a" (syntax-e #'sym) s)))
> (struct-field-info-list
> (syntax-local-value #'sym))
> )])
> #`(quote #,names))]))
>
> ;; This...
> (proc-names A)
> ;; Returns '(A-c A-b)
>
> (define-syntax (names-exist? stx)
> (syntax-case stx ()
> [(_ sym)
> (let ([names (map (λ (s)
> (string->symbol
> (format "~a-~a" (syntax-e #'sym) s)))
> (struct-field-info-list
> (syntax-local-value #'sym))
> )])
> #`(andmap (λ (s)
> (equal? 'lexical s))
> (map (λ (s)
> (defined? s))
> (quote #,names)))
> )]))
>
> (names-exist? A)
> (names-exist? B)
>
>
> On Sat, Oct 30, 2021 at 10:33 PM Brian Beckman <[email protected]>
> wrote:
>
>> 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.
>>>>> >
>>>>> > --
>>>>> > You received this message because you are subscribed to the Google
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>>>>> send an email to [email protected].
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>>>>> https://groups.google.com/d/msgid/racket-users/8e4ca03e-e276-4c42-a662-4fcf7c994387n%40googlegroups.com
>>>>> .
>>>>>
>>>>> --
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>>>>
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>>>> <https://groups.google.com/d/msgid/racket-users/CAK2VK6tMxFH0oEq4iCgk7PW-4yJTB8xNr_b3F6GPwQS1MZVLwQ%40mail.gmail.com?utm_medium=email&utm_source=footer>
>>>> .
>>>>
>>> --
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>> .
>>
> --
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> .
>
--
--
Jens Axel Søgaard
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