Am Sonntag, 24. April 2016 19:29:31 UTC+3 schrieb Matthias Felleisen: > > On Apr 24, 2016, at 9:05 AM, Daniel Karch <[email protected]> wrote: > > > > Hi, > > > > I recently started learning Racket and like it so far. Since I very much > > prefer statically typed languages, I am leaning towards Typed Racket. > > > > In a small program I am writing I would like to have a function that > > accepts a value of an abstract type and then calls a function on that type > > whose implementation depends on the concrete type. I.e., what would be an > > interface in Java with several classes implementing it or a type class in > > Haskell with several instances. > > In vanilla Racket it seems that I could use generic interfaces or > > class-based interfaces, but in TR neither of these options seems to work. > > The following works: > > > > #lang typed/racket > > > > ;; "Interface" > > (define-type X > > (Object [get-name (-> String)])) > > > > ;; Implementation 1 > > (define A% > > (class object% > > (super-new) > > (init-field [name : String]) > > (: get-name (-> String)) > > (define/public (get-name) > > (~a "I am an A% and my name is " name ".")))) > > > > ;; Implementation 2 > > (define B% > > (class object% > > (super-new) > > (init-field [name : String]) > > (: get-name (-> String)) > > (define/public (get-name) > > (~a "I am a B% and my name is " name ".")))) > > > > (: display-name (-> X Void)) > > (define (display-name x) > > (displayln (send x get-name))) > > > > (display-name (make-object A% "Alice")) ;; -> I am an A and my name is > > Alice. > > (display-name (make-object B% "Bob")) ;; -> I am a B and my name is Bob. > > > > – but I am not completely happy about it. Is there an idiomatic way to > > achieve what I described in TR? > > > > Typed Racket does not support ML's abstract types. The goal is primarily to > allow Racket programmers to port existing programs to the typed world in an > incremental fashion. While I consider the existing system usable, there are > many open questions and, frankly, some of them are open research questions, > including how to add expressive power to Typed Racket’s type language that > works with Racket programs. > > Typed Racket also doesn’t support Racket’s interfaces yet, another open > research topic. > > What you have is as close as you can get to what you ask for. Alternatively > experiment with structures (but you seem to come from the OO world, so the > above is good) > > — Matthias
Hello Matthias, thank you for the explanation. I wouldn't say that I come from the OO world – I would much prefer to keep data and functions separate, but I have literally one day of experience with Typed Racket, so the above class-based version was the only way I could get it to work so far. If you could point me towards some resources on how this could be done with structures, that would be great. Best regards Daniel -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
