Re: [racket-users] struct-info
Thanks Matthias, that makes sense.
On Tue, Feb 12, 2019 at 8:50 PM Matthias Felleisen
wrote:
>
>
>
> > On Feb 12, 2019, at 5:28 PM, David Storrs wrote:
> >
> > On Tue, Feb 12, 2019 at 5:03 PM wrote:
>
> This is nice for defining abstract types, but it can be pretty
> inconvenient for defining plain old aggregated data types that just have
> a bundle of fields. When defining those types as structs, consider using
> the #:transparent option. This means "use no inspector at all" (roughly)
> and lets `struct-info` Just Work (TM) without any inspector wrangling.
> The downside is that other modules may be able to break your type's
> invariants and possibly circumvent your contracts.
> >>>
> >>>
> >>> That's what I expected, but it doesn't seem to work:
> >>>
> (struct person (name age) #:transparent)
> (struct-info person)
> >>> #f
> >>> #t
> >>>
> >>> What am I missing?
> >>
> >>
> >> I was stumped on this for a while, but then realized the problem:
> >>
> >>> (struct-info person)
> >> #f
> >> #t
> >>> (struct-info (person "Alyssa P. Hacker" 42))
> >> #
> >> #f
> >
> > Ah, I see. Thanks, I wouldn't have guessed that an instance of a
> > struct satisfied `struct-type?`
> >
> > On the other hand, it seems relatively easy to break these
> > protections. Is there a way to prevent that?
> >
> > ; file test1.rkt
> > #lang racket
> > (struct person (name age))
> > (provide person)
>
>
>
> The line above exports two pieces: the constructor and compile-time
> information about the structure, including the functions as you saw. If you
> want to protect your invariants, you replace this provide with something like
>
>(provide (contract-out (person (-> string natural-number/c person?
>
> See end for a simpler way to test such things.
>
>
>
> > ;; end of test1.rkt
> >
> >
> > ; file test2.rkt
> > #lang racket
> >
> > (require "test1.rkt"
> > (for-syntax racket
> > syntax/parse
> > syntax/parse/experimental/template
> > syntax/parse/class/struct-id))
> >
> > (define p (person 'bob 19))
> > (displayln "required ctor only of a struct defined in another file.
> > Can create, is opaque:")
> > p
> > (displayln "struct-info returns (values #f #t) since the struct isn't
> > inspectable here:")
> > (struct-info p)
> > (define-syntax struct-funcs (syntax-parser [(_ s:struct-id) (template
> > (list s.constructor-id s.accessor-id ...))]))
> > (define lst (struct-funcs person))
> > (displayln "show list of constructor and accessors that we retrieved
> > via macro:")
> > lst
> > (displayln "Fetch name ('bob) by way of accessor returned through macro:")
> > ((second lst) p)
> > ; Uncommenting the following will cause compilation to fail, since
> > person-name was not exported
> > ;(person-name p)
> > ;; end of test2.rkt
> >
> >
> > ;; command line:
> > $ racket test2.rkt
> > required ctor only of a struct defined in another file. Can create, is
> > opaque:
> > #
> > struct-info returns (values #f #t) since the struct isn't inspectable here:
> > #f
> > #t
> > show list of constructor and accessors that we retrieved via macro:
> > '(# # #)
> > Fetch name ('bob) by way of accessor returned through macro:
> > 'bob
> >
> > -
>
>
>
>
> #lang racket
>
> (module test1 racket
> (provide (contract-out (person (-> string natural-number/c person?
> (struct person (name age)))
>
> (module test2 racket
> (require (submod ".." test1)
>(for-syntax racket
>syntax/parse
>syntax/parse/experimental/template
>syntax/parse/class/struct-id))
>
> (define p (person 'bob 19))
> (displayln "required ctor only of a struct defined in another file. Can
> create, is opaque:")
> p
>
> (displayln "struct-info returns (values #f #t) since the struct isn't
> inspectable here:")
> (struct-info p)
>
> (define-syntax struct-funcs (syntax-parser [(_ s:struct-id) (template (list
> s.constructor-id s.accessor-id ...))]))
> (define lst (struct-funcs person))
> (displayln "show list of constructor and accessors that we retrieved via
> macro:")
> lst
>
> (displayln "Fetch name ('bob) by way of accessor returned through macro:")
> ((second lst) p)
>
> ; Uncommenting the following will cause compilation to fail, since
> ; person-name
> )
>
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Re: [racket-users] struct-info
> On Feb 12, 2019, at 5:28 PM, David Storrs wrote:
>
> On Tue, Feb 12, 2019 at 5:03 PM wrote:
This is nice for defining abstract types, but it can be pretty
inconvenient for defining plain old aggregated data types that just have a
bundle of fields. When defining those types as structs, consider using the
#:transparent option. This means "use no inspector at all" (roughly) and
lets `struct-info` Just Work (TM) without any inspector wrangling. The
downside is that other modules may be able to break your type's invariants
and possibly circumvent your contracts.
>>>
>>>
>>> That's what I expected, but it doesn't seem to work:
>>>
(struct person (name age) #:transparent)
(struct-info person)
>>> #f
>>> #t
>>>
>>> What am I missing?
>>
>>
>> I was stumped on this for a while, but then realized the problem:
>>
>>> (struct-info person)
>> #f
>> #t
>>> (struct-info (person "Alyssa P. Hacker" 42))
>> #
>> #f
>
> Ah, I see. Thanks, I wouldn't have guessed that an instance of a
> struct satisfied `struct-type?`
>
> On the other hand, it seems relatively easy to break these
> protections. Is there a way to prevent that?
>
> ; file test1.rkt
> #lang racket
> (struct person (name age))
> (provide person)
The line above exports two pieces: the constructor and compile-time information
about the structure, including the functions as you saw. If you want to protect
your invariants, you replace this provide with something like
(provide (contract-out (person (-> string natural-number/c person?
See end for a simpler way to test such things.
> ;; end of test1.rkt
>
>
> ; file test2.rkt
> #lang racket
>
> (require "test1.rkt"
> (for-syntax racket
> syntax/parse
> syntax/parse/experimental/template
> syntax/parse/class/struct-id))
>
> (define p (person 'bob 19))
> (displayln "required ctor only of a struct defined in another file.
> Can create, is opaque:")
> p
> (displayln "struct-info returns (values #f #t) since the struct isn't
> inspectable here:")
> (struct-info p)
> (define-syntax struct-funcs (syntax-parser [(_ s:struct-id) (template
> (list s.constructor-id s.accessor-id ...))]))
> (define lst (struct-funcs person))
> (displayln "show list of constructor and accessors that we retrieved
> via macro:")
> lst
> (displayln "Fetch name ('bob) by way of accessor returned through macro:")
> ((second lst) p)
> ; Uncommenting the following will cause compilation to fail, since
> person-name was not exported
> ;(person-name p)
> ;; end of test2.rkt
>
>
> ;; command line:
> $ racket test2.rkt
> required ctor only of a struct defined in another file. Can create, is opaque:
> #
> struct-info returns (values #f #t) since the struct isn't inspectable here:
> #f
> #t
> show list of constructor and accessors that we retrieved via macro:
> '(# # #)
> Fetch name ('bob) by way of accessor returned through macro:
> 'bob
>
> -
#lang racket
(module test1 racket
(provide (contract-out (person (-> string natural-number/c person?
(struct person (name age)))
(module test2 racket
(require (submod ".." test1)
(for-syntax racket
syntax/parse
syntax/parse/experimental/template
syntax/parse/class/struct-id))
(define p (person 'bob 19))
(displayln "required ctor only of a struct defined in another file. Can
create, is opaque:")
p
(displayln "struct-info returns (values #f #t) since the struct isn't
inspectable here:")
(struct-info p)
(define-syntax struct-funcs (syntax-parser [(_ s:struct-id) (template (list
s.constructor-id s.accessor-id ...))]))
(define lst (struct-funcs person))
(displayln "show list of constructor and accessors that we retrieved via
macro:")
lst
(displayln "Fetch name ('bob) by way of accessor returned through macro:")
((second lst) p)
; Uncommenting the following will cause compilation to fail, since
; person-name
)
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Re: [racket-users] struct-info
On Tue, Feb 12, 2019 at 5:03 PM wrote:
>>>
>>> This is nice for defining abstract types, but it can be pretty inconvenient
>>> for defining plain old aggregated data types that just have a bundle of
>>> fields. When defining those types as structs, consider using the
>>> #:transparent option. This means "use no inspector at all" (roughly) and
>>> lets `struct-info` Just Work (TM) without any inspector wrangling. The
>>> downside is that other modules may be able to break your type's invariants
>>> and possibly circumvent your contracts.
>>
>>
>> That's what I expected, but it doesn't seem to work:
>>
>> > (struct person (name age) #:transparent)
>> > (struct-info person)
>> #f
>> #t
>>
>> What am I missing?
>
>
> I was stumped on this for a while, but then realized the problem:
>
> > (struct-info person)
> #f
> #t
> > (struct-info (person "Alyssa P. Hacker" 42))
> #
> #f
Ah, I see. Thanks, I wouldn't have guessed that an instance of a
struct satisfied `struct-type?`
On the other hand, it seems relatively easy to break these
protections. Is there a way to prevent that?
; file test1.rkt
#lang racket
(struct person (name age))
(provide person)
;; end of test1.rkt
; file test2.rkt
#lang racket
(require "test1.rkt"
(for-syntax racket
syntax/parse
syntax/parse/experimental/template
syntax/parse/class/struct-id))
(define p (person 'bob 19))
(displayln "required ctor only of a struct defined in another file.
Can create, is opaque:")
p
(displayln "struct-info returns (values #f #t) since the struct isn't
inspectable here:")
(struct-info p)
(define-syntax struct-funcs (syntax-parser [(_ s:struct-id) (template
(list s.constructor-id s.accessor-id ...))]))
(define lst (struct-funcs person))
(displayln "show list of constructor and accessors that we retrieved
via macro:")
lst
(displayln "Fetch name ('bob) by way of accessor returned through macro:")
((second lst) p)
; Uncommenting the following will cause compilation to fail, since
person-name was not exported
;(person-name p)
;; end of test2.rkt
;; command line:
$ racket test2.rkt
required ctor only of a struct defined in another file. Can create, is opaque:
#
struct-info returns (values #f #t) since the struct isn't inspectable here:
#f
#t
show list of constructor and accessors that we retrieved via macro:
'(# # #)
Fetch name ('bob) by way of accessor returned through macro:
'bob
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Re: [racket-users] struct-info
On Tue, Feb 12, 2019 at 3:55 PM David Storrs wrote: > > On Tue, Feb 12, 2019 at 4:46 PM wrote: > >> > >> Thank you for the explanation. Can I ask why the heck it works this > >> way? This seems to be explicitly designed for maximal surprise and > >> minimal usefulness. > > > > > > It works that way so that, by default, modules can't inspect, modify, or > > otherwise muck around with structs defined by other modules. Opaque structs > > (that is, structs that aren't transparent and aren't prefab) aren't really > > meant to be used like "plain old data objects" with fields and accessors, > > they're more like building blocks for abstract data types. A module that > > defines an opaque struct type is expected to be responsible for exporting > > to other modules all the functions that are necessary for using that type. > > Anything not explicitly exported by the module is not allowed, even through > > reflective operations like struct-info. The exception to this rule is when > > some entity above the modules is controlling them all, such as a debugger, > > an IDE, or a server running client-supplied code. In these cases, the > > controlling code has the option to make a child inspector and run all the > > modules under that child inspector, giving the controlling code access to > > all struct types through the parent inspector. This kind of setup can be > > nested arbitrarily deep. > > I see. That makes sense. I think it would be worth expanding the > documentation on that; I'm happy to provide a suggestion later > tonight, but I will need to do it through email instead of via pull > request. I have long since given up on being able to find anything in > the Racket github in order to provide patches. It's simply too > unintuitive and time-intensive to find the relevant section in > multiple repositories where the documentation is in randomly-named > fragments scattered across multiple directories instead of being > individual files with guessable names. > > > > > > This is nice for defining abstract types, but it can be pretty inconvenient > > for defining plain old aggregated data types that just have a bundle of > > fields. When defining those types as structs, consider using the > > #:transparent option. This means "use no inspector at all" (roughly) and > > lets `struct-info` Just Work (TM) without any inspector wrangling. The > > downside is that other modules may be able to break your type's invariants > > and possibly circumvent your contracts. > > That's what I expected, but it doesn't seem to work: > > > (struct person (name age) #:transparent) > > (struct-info person) > #f > #t > > What am I missing? > It takes an instance of person. (struct-info (person "Me" 3.14)) FWIW if you already have the struct type descriptor (which is what struct-info returns), you can directly call struct-type-info. (struct-type-info (let-values ([(desc skip?) (struct-info (person "Me" 3.14))]) desc)) ;; struct:person is introduced by the (struct person ...) form (struct-type-info struct:person) > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] struct-info
> > This is nice for defining abstract types, but it can be pretty >> inconvenient for defining plain old aggregated data types that just have a >> bundle of fields. When defining those types as structs, consider using the >> #:transparent option. This means "use no inspector at all" (roughly) and >> lets `struct-info` Just Work (TM) without any inspector wrangling. The >> downside is that other modules may be able to break your type's invariants >> and possibly circumvent your contracts. > > > That's what I expected, but it doesn't seem to work: > > > (struct person (name age) #:transparent) > > (struct-info person) > #f > #t > > What am I missing? > I was stumped on this for a while, but then realized the problem: > (struct-info person) #f #t > (struct-info (person "Alyssa P. Hacker" 42)) # #f -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] struct-info
> > Thank you for the explanation. Can I ask why the heck it works this > way? This seems to be explicitly designed for maximal surprise and > minimal usefulness. > It works that way so that, by default, modules can't inspect, modify, or otherwise muck around with structs defined by other modules. Opaque structs (that is, structs that aren't transparent and aren't prefab) aren't really meant to be used like "plain old data objects" with fields and accessors, they're more like building blocks for abstract data types. A module that defines an opaque struct type is expected to be responsible for exporting to other modules all the functions that are necessary for using that type. Anything not explicitly exported by the module is not allowed, even through reflective operations like struct-info. The exception to this rule is when some entity *above* the modules is controlling them all, such as a debugger, an IDE, or a server running client-supplied code. In these cases, the controlling code has the option to make a child inspector and run all the modules under that child inspector, giving the controlling code access to all struct types through the parent inspector. This kind of setup can be nested arbitrarily deep. This is nice for defining abstract types, but it can be pretty inconvenient for defining plain old aggregated data types that just have a bundle of fields. When defining those types as structs, consider using the #:transparent option. This means "use no inspector at all" (roughly) and lets `struct-info` Just Work (TM) without any inspector wrangling. The downside is that other modules may be able to break your type's invariants and possibly circumvent your contracts. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] struct-info
On Tue, Feb 12, 2019 at 11:43 AM Shu-Hung You wrote: > > On Tue, Feb 12, 2019 at 10:04 AM David Storrs wrote: > > > > Could someone point me to the FM on how to properly use struct-info? > > For the life of me, I cannot get anything except (values #f #t) out of > > it. I see that: > > > > 1) struct-info only works with struct types that are under the control > > of the current inspector. > > > > 2) You can provide an inspector to a struct declaration, but it will > > be placed under the control of the **parent** of what you passed it, > > not the actual thing you passed it. This breaks my brain. > > > > The inspector used at struct type creation time needs to be controlled > by the current inspector so you can obtain reflective information. > That is, the inspector used at struct type creation time is a > sub(-sub-sub-...) inspector of the current inspector. > > #lang racket/base > > (require racket/struct-info) > > (define old-insp (current-inspector)) > (define insp (make-inspector)) > > (current-inspector insp) > (struct S (field1 field2)) > (current-inspector old-insp) > > (define s > (S 5 'hi)) > > (struct-info s) ;;=> ok > > (current-inspector insp) > (struct-info s) ;;=> #f #t Thank you for the explanation. Can I ask why the heck it works this way? This seems to be explicitly designed for maximal surprise and minimal usefulness. > > > > -- > > You received this message because you are subscribed to the Google Groups > > "Racket Users" group. > > To unsubscribe from this group and stop receiving emails from it, send an > > email to racket-users+unsubscr...@googlegroups.com. > > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[racket-users] struct-info
Could someone point me to the FM on how to properly use struct-info? For the life of me, I cannot get anything except (values #f #t) out of it. I see that: 1) struct-info only works with struct types that are under the control of the current inspector. 2) You can provide an inspector to a struct declaration, but it will be placed under the control of the **parent** of what you passed it, not the actual thing you passed it. This breaks my brain. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
