Then is there something like and/c for types? (like U is like or/c for types)
That could probably solve it.
It seems like typed racket is already doing this in some cases, for example:
#lang typed/racket
(define positive-real? (make-predicate Positive-Real))
(define (f x)
(if (positive-real? x)
(if (exact-integer? x)
x
(error "error"))
(error "error")))
> f
- : (Any -> Positive-Integer)
#<procedure:f>
In this, typed racket figures out that f produces a Positive-Integer, when it
was only given that it produces something that is both a Positive-Real and an
Integer.
But I couldn’t find it in the docs.
On Apr 25, 2014, at 10:48 PM, Sam Tobin-Hochstadt <sa...@cs.indiana.edu> wrote:
> What you're looking for is called bounded polymorphism. Sadly, Typed Racket
> doesn't support this, so I'd try one of the options David suggests.
>
> Sam
>
> On Apr 25, 2014 10:46 PM, "Alexander D. Knauth" <alexan...@knauth.org> wrote:
> That’s what I tried at first, but my actual struct is a lot more complicated
> than posn, and it kept giving be type-check errors, and trying to enforce the
> types of the fields myself just ended up with completely unreadable code and
> even more type errors, so I gave up on making it polymorphic, but I still
> wanted to be able to specify specific cases of it as types that would only
> contain that specific case of it.
>
> On Apr 25, 2014, at 10:25 PM, David Van Horn <dvanh...@cs.umd.edu> wrote:
>
> > On 4/25/14, 9:57 PM, Alexander D. Knauth wrote:
> >> But then the posn constructor doesn’t enforce that it’s arguments have to
> >> be Reals, and the posn? predicate doesn’t check it, and the accessors
> >> don’t say that they always produce Reals.
> >
> > Maybe I'm not seeing the big picture, but that's what the Posn type is
> > for. If you apply posn to something other than reals, you won't get a
> > Posn. If you have a Posn and apply posn-x, you get a real.
> >
> > (define: (f [p : Posn]) : Real
> > (+ (posn-x p) (posn-y p)))
> >
> > David
> >
> >
> >> On Apr 25, 2014, at 9:49 PM, David Van Horn <dvanh...@cs.umd.edu> wrote:
> >>
> >>> How about this?
> >>>
> >>> (struct: (x y) posn ([x : x] [y : y]))
> >>> (define-type Posn (posn Real Real))
> >>> (define-type Origin (posn Zero Zero))
> >>>
> >>>
> >
>
>
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