[racket] Question about Typed Racket

I don't think you're doing anything wrong, and I expect that this case
[1] needs a bit of generalization to handle polymorphic structs.

[1] https://github.com/racket/typed-racket/blob/master/typed-racket-lib/typed-racket/typecheck/tc-app/tc-app-hetero.rkt#L82-L83

Sam

On Thu, Feb 12, 2015 at 8:21 PM, Antonio Menezes Leitao
<antonio.menezes.leitao at ist.utl.pt> wrote:
> Hi,
>
> The following example works in Typed Racket:
>
> (struct foo
>   ([c : Float]
>    [f : (foo -> Float)]))
>
> (define (test [f : foo]) : Float
>   ((foo-f f) f))
>
> (test
>  (foo 1.0
>       (lambda ([x : foo]) : Float
>         (match x ((foo c _) c)))))
>
> (struct bar foo
>   ([i : Float]))
>
> (test
>  (bar 1.0
>       (lambda ([x : foo]) : Float
>         (match x
>           ((bar c _ i) (+ c i))))
>       1.0))
>
>
> Unfortunately, I couldn't make foo polymorphic:
>
> (struct (R) foo
>   ([c : R]
>    [f : ((foo R) -> R)]))
>
> (define (test [f : (foo Float)]) : Float
>   ((foo-f f) f))
>
> (test
>  (foo 1.0
>       (lambda ([x : (foo Float)]) : Float
>         (match x
>           ((foo c _) c)))))
>
> (struct (R) bar foo
>   ([i : Float]))
>
> (test
>  (bar 1.0
>       (lambda ([x : (foo Float)]) : Float
>         (match x
>           ((bar c _ i) (+ c i))))
>       1.0))
>
> The problem is in the match in the last expression, which shows three type
> errors:
>
> Type Checker: cannot apply a function with unknown arity; function
> `unsafe-struct-ref' has type Procedure which cannot be applied in: (match x
> ((bar c _ i) (+ c i)))
>   #(364 41)
>
> Can someone tell me what I'm doing wrong here?
>
> Thanks,
> António.
>
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