Classes:
cool, so I can make a function that produces a polymorphic subclass of C1,
but not a straight polymorphic subclass. I can work with that.
It seems in this case, if I want to implement a new method for the subclass
C2 I can not use
```
(define-type (D-class A)(Class ... #:implements (C-class A) ...)
```
Or is there also a special way to make this work?
If not, at least I can define a new type in which I copy the complete Class
type again + the new method, so it's not a big problem.
Structs:
what I got working was this:
```
#lang typed/racket/base
(struct (A) S ([f1 : (-> A A A)]
[f2 : (-> Any Boolean : #:+ A)])
#:prefab
)
(: S-of-type? (All (A) (-> Any
(-> Any Boolean : #:+ A)
Boolean
: #:+ (implies #t (S A)))))
(define (S-of-type? obj fct) (and (S? obj)(eq? fct (S-f2 obj))))
(define C ((inst S Number) + number?))
(S-of-type? C number?)
(S-of-type? C real?)
```
It works on a prefab structure, but not on a normal structure. I was hoping
to use this as a way to get the type at runtime. But since it only works
with prefab structures, It doesn't work... (or better said, too many
objects can pass this test).
For a normal structure I hoped the guarantee that it was created with (S
...) would be enough extra info to be sure that if f2 is eq? then S must be
of type A for f2 of type (-> Any Boolean : #:+ A)
But anyway, I feel that for what I need, classes are really the better
option, so I will try to type it with the tip you gave me, or if that
doesn't work, go for untyped.
Thank you very much,
Bert
On Monday, 18 November 2019 20:30:09 UTC+1, Sam Tobin-Hochstadt wrote:
>
> It is possible to get the contracts of values, (see `value-contract`)
> but Typed Racket doesn't know how to do that, and it would be
> problematic anyway since the value isn't around until runtime, but TR
> runs at compile time.
>
> Sam
>
> On Mon, Nov 18, 2019 at 12:24 PM David Storrs <david...@gmail.com
> <javascript:>> wrote:
> >
> >
> >
> > On Mon, Nov 18, 2019 at 12:23 PM David Storrs <david...@gmail.com
> <javascript:>> wrote:
> >>
> >>
> >>
> >> On Mon, Nov 18, 2019 at 10:09 AM Sam Tobin-Hochstadt <
> sa...@cs.indiana.edu <javascript:>> wrote:
> >>>
> >>>
> >>> Third, your version with structs can't work because you can't tell
> >>> what type a function expects -- that information is not there at
> >>> runtime.
> >>
> >>
> >> If there is a contract assigned to a function, is it possible to get
> that function and analyze it?
> >
> >
> > Correction: Get that *contract* and analyze it.
> >
> >>
> >>>
> >>> Sam
> >>>
> >>> On Wed, Nov 6, 2019 at 2:51 PM bedeke <bed...@hotmail.com
> <javascript:>> wrote:
> >>> >
> >>> > Hello,
> >>> >
> >>> > I was trying to type some polymorphic classes but I got stuck early
> on making a polymorphic subclass
> >>> >
> >>> > #lang typed/racket/base
> >>> >
> >>> > ;*****1*****
> >>> > (require typed/racket/class)
> >>> >
> >>> > (define-type (C-class A)(Class [init-field [x A]]))
> >>> >
> >>> > (define C1%
> >>> > (class object%
> >>> > #:∀ (A)
> >>> > (init-field [x : A])
> >>> > (super-new)))
> >>> >
> >>> > (define C2%
> >>> > (class (inst C1% A)
> >>> > #:∀ (A)
> >>> > (super-new)))
> >>> >
> >>> > (new (inst C2% Integer) [x 4])
> >>> >
> >>> > C1% is recognised as a C-class, but explicitly calling C1% a C-class
> (omitting the #:forall (A) ) doesn't work
> >>> > In the next step I don't seem to find the right way to make C2% a
> polymorphic subclass of C1%
> >>> >
> >>> >
> >>> >
> >>> > Having failed that I went with structures. This I got mostly
> working, but I would like to have some niceties.
> >>> > One was to parameterize a structure, but this lead to a problem of
> not being able to check some
> >>> > types at runtime. I thought I got close, but I stranded on getting
> fields of structures without knowing the instantiation type
> >>> > ;*****2*****
> >>> > (struct (A) S ([f1 : (-> A A A)]
> >>> > [f2 : (-> A Boolean : A)]))
> >>> >
> >>> > (: S-of-type? (-> (-> Any Boolean : A) Any Boolean
> >>> > : #:+ (implies #t (S A))
> >>> > #:- (implies #f (! (S A)))))
> >>> > (define (S-of-type? fct A)
> >>> > (and (S? A) (eq? fct (S-f2 A))))
> >>> > ; ^ how can I acces a field of this polymorfic
> struct
> >>> >
> >>> >
> >>> >
> >>> > And another thing I tried but failed to get working is to sub-type a
> structure based
> >>> > on a narrower type for one of the fields.
> >>> > ;*****3*****
> >>> > (struct (A) B ([f1 : (Vectorof A)]
> >>> > [f2 : Integer])
> >>> > #:transparent)
> >>> >
> >>> > (: B1? (All (A) (-> (B A) Boolean)))
> >>> > (define (B1? b)(= (B-f2 b) 1))
> >>> > (define b (B (vector 3) 1))
> >>> > (assert b B1?)
> >>> > b
> >>> > (define-type B1 B1?)
> >>> > ;(define-new-subtype B1 B1?)
> >>> > ;(define-type B1 (All (A)(Struct (B (Vectorof A) 1))))
> >>> >
> >>> >
> >>> > Are any of these things doable? Or are there better ways to tackle
> this problems?
> >>> >
> >>> >
> >>> > What I got working is in
> >>> >
> https://github.com/bdeket/polynomials/blob/alg-dic-pol/polynomials/math/private/polynomial/poly-struct.rkt
>
> (WIP)
> >>> >
> >>> > Kind regards,
> >>> > Bert
> >>> >
> >>> > --
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>
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