[racket] Unexpected results with impersonators and make-keyword-procedure

[Scott Moore]

Hi,

I've run into some strange behavior with the interaction between
impersonators and make-keyword-procedure. I expect that when not invoked
with keywords, the result of make-keyword-procedure and a lambda with the
same form should be equivalent. Instead, they behave differently when
impersonated. I have included a small module that demonstrates the issue
below. I expect that the two checks at the bottom should succeed.

Thanks,
Scott

#lang racket

(require rackunit)

(define-values (prop:my-prop my-prop? my-prop-accessor)
(make-impersonator-property 'my-prop))

(define (mark-with-my-prop val)
(impersonate-procedure
val
#f
prop:my-prop
#t))

(define (mark-fun-mkp f)
(mark-with-my-prop
(make-keyword-procedure
(λ (kwds kwd-args . other-args)
(keyword-apply f kwds kwd-args other-args))
(λ args
(apply f args)))))

(define (mark-fun-lambda f)
(mark-with-my-prop
(λ args
(apply f args))))

(define (dummy-impersonator val)
(make-keyword-procedure
(λ (kwds kwd-args . other-args)
(apply values kwd-args other-args))
(λ args
(apply values args))))

(define marked-mkp (mark-fun-mkp display))
(define marked-lambda (mark-fun-lambda display))

(check-eq? (my-prop? marked-lambda) (my-prop? marked-mkp))
(check-eq? (my-prop? (impersonate-procedure marked-lambda
(dummy-impersonator marked-lambda)))
(my-prop? (impersonate-procedure marked-mkp (dummy-impersonator
marked-mkp))))

[Matthew Flatt]

I agree that this is a bug --- specific to impersonators that are not
chaperones --- and I've pushed a repair to the Git repo.

The general repair was to make impersonator-property predicates and
accessors sensitive to `prop:impersonator-of`. When a structure
impersoator does not have a particular impersonator property, but its
structure has the `prop:impersonator-of` property, then the structure
produced by `prop:impersonator-of` is checked (recursively). That
change fixes the problem with keyword procedures, because
`impersonator-procedure` on keyword-acepting procedure is implemented
through an internal structure type that has `prop:impersonator-of`.

Thanks for the report!

Post by Scott Moore
Hi,
I've run into some strange behavior with the interaction between
impersonators and make-keyword-procedure. I expect that when not invoked
with keywords, the result of make-keyword-procedure and a lambda with the
same form should be equivalent. Instead, they behave differently when
impersonated. I have included a small module that demonstrates the issue
below. I expect that the two checks at the bottom should succeed.
Thanks,
Scott
#lang racket
(require rackunit)
(define-values (prop:my-prop my-prop? my-prop-accessor)
(make-impersonator-property 'my-prop))
(define (mark-with-my-prop val)
(impersonate-procedure
val
#f
prop:my-prop
#t))
(define (mark-fun-mkp f)
(mark-with-my-prop
(make-keyword-procedure
(λ (kwds kwd-args . other-args)
(keyword-apply f kwds kwd-args other-args))
(λ args
(apply f args)))))
(define (mark-fun-lambda f)
(mark-with-my-prop
(λ args
(apply f args))))
(define (dummy-impersonator val)
(make-keyword-procedure
(λ (kwds kwd-args . other-args)
(apply values kwd-args other-args))
(λ args
(apply values args))))
(define marked-mkp (mark-fun-mkp display))
(define marked-lambda (mark-fun-lambda display))
(check-eq? (my-prop? marked-lambda) (my-prop? marked-mkp))
(check-eq? (my-prop? (impersonate-procedure marked-lambda
(dummy-impersonator marked-lambda)))
(my-prop? (impersonate-procedure marked-mkp (dummy-impersonator
marked-mkp))))
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[Scott Moore]

Hi Matthew,

Thanks for working on this so quickly! Unfortunately, It looks like there is a bug in the fix that causes segfaults when checking impersonator properties on keyword procedures that are not impersonators. I’ve included a small test case below.

Thanks again,
Scott

#lang racket

(define-values (prop:my-prop my-prop? my-prop-accessor)
(make-impersonator-property 'my-prop))

(define kwp
(make-keyword-procedure
(λ (kwds kwd-args . other-args)
(printf "Keywords: ~a~n" kwds)
(printf "Keyword arguments: ~a~n" kwd-args)
(printf "Other arguments: ~a~n" other-args))
(λ args
(printf "Arguments: ~a~n" args))))

(my-prop? kwp)

Post by Matthew Flatt
I agree that this is a bug --- specific to impersonators that are not
chaperones --- and I've pushed a repair to the Git repo.
The general repair was to make impersonator-property predicates and
accessors sensitive to `prop:impersonator-of`. When a structure
impersoator does not have a particular impersonator property, but its
structure has the `prop:impersonator-of` property, then the structure
produced by `prop:impersonator-of` is checked (recursively). That
change fixes the problem with keyword procedures, because
`impersonator-procedure` on keyword-acepting procedure is implemented
through an internal structure type that has `prop:impersonator-of`.
Thanks for the report!

Post by Scott Moore
Hi,
I've run into some strange behavior with the interaction between
impersonators and make-keyword-procedure. I expect that when not invoked
with keywords, the result of make-keyword-procedure and a lambda with the
same form should be equivalent. Instead, they behave differently when
impersonated. I have included a small module that demonstrates the issue
below. I expect that the two checks at the bottom should succeed.
Thanks,
Scott
#lang racket
(require rackunit)
(define-values (prop:my-prop my-prop? my-prop-accessor)
(make-impersonator-property 'my-prop))
(define (mark-with-my-prop val)
(impersonate-procedure
val
#f
prop:my-prop
#t))
(define (mark-fun-mkp f)
(mark-with-my-prop
(make-keyword-procedure
(λ (kwds kwd-args . other-args)
(keyword-apply f kwds kwd-args other-args))
(λ args
(apply f args)))))
(define (mark-fun-lambda f)
(mark-with-my-prop
(λ args
(apply f args))))
(define (dummy-impersonator val)
(make-keyword-procedure
(λ (kwds kwd-args . other-args)
(apply values kwd-args other-args))
(λ args
(apply values args))))
(define marked-mkp (mark-fun-mkp display))
(define marked-lambda (mark-fun-lambda display))
(check-eq? (my-prop? marked-lambda) (my-prop? marked-mkp))
(check-eq? (my-prop? (impersonate-procedure marked-lambda
(dummy-impersonator marked-lambda)))
(my-prop? (impersonate-procedure marked-mkp (dummy-impersonator
marked-mkp))))
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[Matthew Flatt]

Oops... I'll push a repair soon.

Thanks!

Post by Scott Moore
Hi Matthew,
Thanks for working on this so quickly! Unfortunately, It looks like there is a
bug in the fix that causes segfaults when checking impersonator properties on
keyword procedures that are not impersonators. I’ve included a small test case
below.
Thanks again,
Scott
#lang racket
(define-values (prop:my-prop my-prop? my-prop-accessor)
(make-impersonator-property 'my-prop))
(define kwp
(make-keyword-procedure
(λ (kwds kwd-args . other-args)
(printf "Keywords: ~a~n" kwds)
(printf "Keyword arguments: ~a~n" kwd-args)
(printf "Other arguments: ~a~n" other-args))
(λ args
(printf "Arguments: ~a~n" args))))
(my-prop? kwp)

Post by Matthew Flatt
I agree that this is a bug --- specific to impersonators that are not
chaperones --- and I've pushed a repair to the Git repo.
The general repair was to make impersonator-property predicates and
accessors sensitive to `prop:impersonator-of`. When a structure
impersoator does not have a particular impersonator property, but its
structure has the `prop:impersonator-of` property, then the structure
produced by `prop:impersonator-of` is checked (recursively). That
change fixes the problem with keyword procedures, because
`impersonator-procedure` on keyword-acepting procedure is implemented
through an internal structure type that has `prop:impersonator-of`.
Thanks for the report!

Post by Scott Moore
Hi,
I've run into some strange behavior with the interaction between
impersonators and make-keyword-procedure. I expect that when not invoked
with keywords, the result of make-keyword-procedure and a lambda with the
same form should be equivalent. Instead, they behave differently when
impersonated. I have included a small module that demonstrates the issue
below. I expect that the two checks at the bottom should succeed.
Thanks,
Scott
#lang racket
(require rackunit)
(define-values (prop:my-prop my-prop? my-prop-accessor)
(make-impersonator-property 'my-prop))
(define (mark-with-my-prop val)
(impersonate-procedure
val
#f
prop:my-prop
#t))
(define (mark-fun-mkp f)
(mark-with-my-prop
(make-keyword-procedure
(λ (kwds kwd-args . other-args)
(keyword-apply f kwds kwd-args other-args))
(λ args
(apply f args)))))
(define (mark-fun-lambda f)
(mark-with-my-prop
(λ args
(apply f args))))
(define (dummy-impersonator val)
(make-keyword-procedure
(λ (kwds kwd-args . other-args)
(apply values kwd-args other-args))
(λ args
(apply values args))))
(define marked-mkp (mark-fun-mkp display))
(define marked-lambda (mark-fun-lambda display))
(check-eq? (my-prop? marked-lambda) (my-prop? marked-mkp))
(check-eq? (my-prop? (impersonate-procedure marked-lambda
(dummy-impersonator marked-lambda)))
(my-prop? (impersonate-procedure marked-mkp (dummy-impersonator
marked-mkp))))
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