Hi Scott,
This is cool!
On 2016-01-27 14:05:10 -0500, Scott Moore wrote:
> This does not quite achieve bounded parametric polymorphism because
> there is no check that all values flowing through the same type
> variable have the same type.
I think there is another sense in which it's not quite parametric (or at least
it's different from parametric->/c). Here's an example:
Welcome to Racket v6.4.0.4.
-> (require bounded)
-> (struct foo (x) #:property prop:procedure 0)
-> (define/contract (check fn val)
(bounded-polymorphic->/c ([X (integer? . -> . integer?)]) (X any/c .
-> . X))
;; I thought this would error rather than succeeding
(displayln (foo-x fn))
fn)
-> (check (foo (lambda (x) 3)) 3)
#<procedure>
#<procedure>
How I imagined this might work is that you would wrap the value so that you can
only make observations corresponding to the bound. So here you force the `foo`
to act only as an int function, masking its structness since that's a finer
distinction than the bound gives you.
Also it's interesting that only higher-order contracts are accepted as bounds.
I guess because you need to stamp the value as belonging to X while still
allowing operations on it? (which you couldn't do on a symbol, say)
Cheers,
Asumu
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