plot-pict does not return a typed/pict type

[bennn]

On Racket v6.4.0.15, this code fails to compile. Casting p to a pict type makes the program compile and run, but the cast shouldn't be necessary.

#lang typed/racket/base

(require plot/typed/no-gui
         typed/pict)

(define p (plot-pict '() #:x-min 0 #:x-max 0 #:y-min 0 #:y-max 0))
(hc-append 0
           p
           (blank 0 0))

The error message

Type Checker: type mismatch
  expected: pict
  given: Pict
  in: p

[alex-hhh]

Hi @samth , I might need your advice on this issue. This is still a problem in Racket 7.7. The type Pict is defined in

plot/plot-lib/plot/private/no-gui/evil-types.rkt

Line 7 in 6a593ce

[#:opaque Pict pict?])

Was this done before the pict library was typed? Is this still needed?

[samth]

Yes, I believe that code predates typed/pict. I'm sure I have some code lying around that fixes this, but I think it's not backwards compatible in other ways, which is why it didn't get merged. Unfortunately, I can't find it at the moment. I think the short answer is that this is likely to stay a bug for a while yet unless it's really a blocker for someone.

[gpitton]

I might have found a related issue (pasting from the CLI, Racket 8.0 CS):

> bins
- : (Vectorof
     (U (Immutable-Vector Flonum Integer) (Mutable-Vector Flonum Integer)))

> (plot (discrete-histogram bins))
. Type Checker: type mismatch
  expected: (Sequenceof
             (U (Immutable-Vector Any (U False Real ivl))
                (List Any (U False Real ivl))
                (Mutable-Vector Any (U False Real ivl))))
  given: (Vectorof
          (U (Immutable-Vector Flonum Integer)
             (Mutable-Vector Flonum Integer))) in: bins

Could somebody confirm?

[bdeket]

Related to the original question, and not what @gpitton reported:
In Pr #90 I edited the evil-typed.rkt to re-export pict from typed/pict as Pict instead of creating the opaque type.
I hope I didn't break anything doing that. But with this change, the original example works.

[samth]

@gpitton That isn't a bug, the problem is that mutable vectors are not subtypes in the way you are expecting in that code. You can't supply a (Mutable-Vector Flonum Integer) when you need a (Mutable-Vector Any (U False Real ivl)). That's because discrete-histogram could (but doesn't) mutate the input to have 'x as the 0th element of the inner vector, violating the type of bins.

Depending on how you're constructing bins, you might be able to use vector-immutable to just have immutable vectors and then it will work.

[gpitton]

Depending on how you're constructing bins, you might be able to use vector-immutable to just have immutable vectors and then it will work.

@samth Thanks! I am not sure I understand why the type checking failed, but this is how I was generating the vector:

(define bins
  (for/vector : (Vectorof (Vector Float Integer))
      ([lb (in-list bounds)] ;; lb is a Float
       [c (in-list rw-counts)])  ;; c is an Integer
      (vector (f lb) c)))  ;; f is a function Float -> Float

and this is how I fixed it:

(define bins
  (for/vector : (Vectorof (Immutable-Vector Float Integer))
      ([lb (in-list bounds)]
       [c (in-list rw-counts)])
      (vector-immutable (f lb) c)))

As expected, the new type signature is:

> bins
- : (Vectorof (Immutable-Vector Flonum Integer))

Now everything works fine, so I take back my previous report.

[alex-hhh]

This was fixed by #90, and this change will make it in Racket 8.1. All packages on pkgs.racket-lang.org were already built with this change and I am not aware of any regressions. I will close this issue, since ultimately this is the intended behavior.