Pict and pict types

[Tim Jervis]

Hi everyone,

In typed racket, vc-append expects arguments of type pict, while plot-pict produces results of type Pict. Therefore, to have vc-append accept a plot-pict argument, I’m currently casting the result of plot-pict to be of type pict.

From my understanding of the underlying racket code, Pict just invokes a pict? predicate through an #opaque definition, and cast inserts a runtime test of its argument. Therefore, my cast seems wasteful. Have I missed something? Is there a better way to structure a solution that type-checks?

Here’s some code that type-checks for me:

#lang typed/racket

(require plot

         pict)

(vc-append (cast (plot-pict (function sin 0 1))

                 pict))

and the output is a graph, as expected.

Here’s some that fails a type-check:

#lang typed/racket

(require plot

         pict)

(vc-append (plot-pict (function sin 0 1)))

Error output:

;  plot-pict-test.rkt:6:11: Type Checker: type mismatch

;   expected: pict

;   given: Pict

;   in: (plot-pict (function sin 0 1))

; Context (plain; to see better errortrace context, re-run with C-u prefix):

;   /Applications/Racket/share/pkgs/typed-racket-lib/typed-racket/typecheck/tc-toplevel.rkt:376:0 type-check

;   /Applications/Racket/share/pkgs/typed-racket-lib/typed-racket/typecheck/tc-toplevel.rkt:619:0 tc-module

;   /Applications/Racket/share/pkgs/typed-racket-lib/typed-racket/tc-setup.rkt:96:12

;   /Applications/Racket/share/pkgs/typed-racket-lib/typed-racket/typed-racket.rkt:23:4

I get the same results whether I require pict or typed/pict.

I hope this question is of general interest. I have some familiarity with regular racket, but I’m only just starting out on typed racket. 

Best,

Tim

[Alex Harsanyi]

This is a known issue:  plot-pict does not return a typed/pict type · Issue #15 · racket/plot (github.com)  

Alex.