Re: TR warning with pict3d-canvas% (in pict3d)

On Wed, Sep 7, 2016 at 10:35 AM, Tim Brown <[email protected]> wrote:

> ffi-types.rkt:19 is:
>  ..
>  17  (require/typed
>  18   ffi/unsafe
> *19   [#:opaque CPointer cpointer?]  ; includes Bytes and other things
> that can be used as cpointers
>  20   [#:opaque CType ctype?]
>  21   )
>  ..
> which seems perfectly innocuous to me :-/
>

You're right, it's innocuous. So we can use `unsafe-require/typed`:

#lang typed/racket/base
(require (only-in typed/racket/unsafe unsafe-require/typed))

(unsafe-require/typed ffi/unsafe
  [#:opaque CPointer cpointer?]
  [#:opaque CType ctype?]
)
(require/typed ffi/unsafe
  [malloc (-> Fixnum CPointer)]
)

(malloc 4) ;; no warnings


---

Here's the discussion behind the warning messages:
https://github.com/racket/typed-racket/pull/396

Basically, the trouble is that `cpointer?` might be an evil untyped
function:

(define (cpointer? x)
  (when (box? x)
    (set-box! x 'EVIL))
  #t)


Typed Racket can't be sure, so it tries to protect all arguments to
`cpointer?`.
But when you call `(cpointer? v)` where `v` is a `#<cpointer>`, Typed
Racket warns you that it doesn't know how to protect `#<cpointer>` values.

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