invalid memory error from parameter with contracted guard

[David Storrs]

I'm seeing an "invalid memory reference.  Some debugging context lost" error when using a parameter that has a guard function AND the guard function is user-defined AND the guard function has a contract on it.  What is the right place to file this aside from the list?

Demonstration:

#lang racket/base

(require racket/contract)

(define p1 (make-parameter ""))
(displayln "before set p1")
(p1 "ok")
(displayln "before read p1")
(p1)

(define/contract p2 (parameter/c string?) (make-parameter ""))
(displayln "before set p2")
(p2 "ok")
(displayln "before read p2")
(p2)


(define/contract p3 (parameter/c string? integer?) (make-parameter "7" string->number ))
(displayln "before set p3")
(p3 "8")
(displayln "before read p3")
(p3)

(define (uncontracted-string->number v)

  (string->number v))

(define/contract (contracted-string->number v)
  (-> string? number?)
  (string->number v))

(define/contract p4  (parameter/c string? integer?)  (make-parameter "7" uncontracted-string->number))
(displayln "before set p4")
(p4 "8")
(displayln "before read p4")
(p4)

(define/contract p5  (parameter/c string? integer?)  (make-parameter "7" contracted-string->number))
(displayln "before set p5")
(p5 "8")
(displayln "before read p5")
(p5) ; invalid memory reference.  Some debugging context lost                                      

[Gustavo Massaccesi]

The list is fine, but sometimes messages are forgotten because it's difficult to track them.

If you have a GitHub account, it's better to post is as an issue in https://github.com/racket/racket

Gustavo

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[Matthew Flatt]

Hi David,

Thanks for the report! This is fixed for the next release and in
the current snapshots.

The repair was commit

cb959879de21406571fb0127ded88c54e171c0eb

See also https://github.com/racket/racket/issues/3865


Matthew

[David Storrs]

Great! You're the best, Matt.  What was the issue, if it's simple enough to explain?

[Matthew Flatt]

Procedures with contracts are usually implemented by structs that have
`prop:procedure`. Those applicable structs are not procedures from Chez
Scheme's perspective. So, in the "Rumble" layer that bridges Chez
Scheme and Racket, care must be taken to use a special `|#%app|` form
instead of direct function application when the function to call might
be from the Racket layer and implemented as an applicable struct.

Parameters are implemented in the Rumble layer, but applying a
parameter's guard procedure didn't use `|#%app|` as it should have. The
repair was to add `|#%app|`.

[David Storrs]

Got it. Thank you.