A quick example:
#lang racket
(require racket/require)
(require (filtered-in (λ (name) (regexp-replace #rx"struct[+][+]" name
"struct"))
struct-plus-plus))
(struct horse (breed color legs))
(define beauty (horse 'arabian 'black 4))
(define info (force (struct-ref beauty)))
(map struct-field-name (struct-info-fields info))
The result is:
'(breed color legs)
Den søn. 31. okt. 2021 kl. 13.06 skrev David Storrs <[email protected]
>:
>
>
> On Sun, Oct 31, 2021, 7:49 AM Jens Axel Søgaard <[email protected]>
> wrote:
>
>> 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
>>
>
> Coincidentally, that module exists!
>
>
> https://docs.racket-lang.org/struct-plus-plus/index.html#%28part._.Reflection%29
>
>
>
>>
>>
>> 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
>>>>>>> Groups "Racket Users" group.
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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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>>>>>> To unsubscribe from this group and stop receiving emails from it,
>>>>>> send an email to [email protected].
>>>>>>
>>>>> 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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>>>> .
>>>>
>>> --
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>>> To view this discussion on the web visit
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>>> .
>>>
>>
>>
>> --
>> --
>> Jens Axel Søgaard
>>
>> --
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>>
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--
--
Jens Axel Søgaard
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