Thank you. The `prop:procedure` works as hoped, in that the class instance becomes usable in any form that takes a procedure (including things like map).
The `prop:sequence` also works, but … what it seems I really want is `prop:list`, which AFAICT doesn't exist (?) The class I'm making is basically a list wrapped with some state. So in terms of the class interface, it would be very convenient to allow a class instance to be used anywhere a list is used. The problem with `prop:sequence` is that now I have to use the special sequence versions of list functions, or convert to a list explicitly with `sequence->list`. In terms of class interface, this isn't an improvement over just using a method like (send class-instance get-list). On Thu, Oct 2, 2014 at 7:43 PM, Alexander D. Knauth <alexan...@knauth.org> wrote: > I don’t know if you can do it with generic interfaces (as in > racket/generic), > but you can make classes whose instances have struct-type properties such > as prop:procedure and prop:sequence > (using interfaces as in racket/class, not racket/generic) > > #lang racket > > (define proc<%> > (interface* () > ([prop:procedure > (lambda (this . args) > (send/apply this proc args))]) > proc)) > > (define proc% > (class* object% (proc<%>) > (super-new) > (define/public (proc x) > (displayln "this is the proc method of proc%") > x))) > > (define seq<%> > (interface* () > ([prop:sequence > (lambda (this) > (send this get-sequence))]) > get-sequence)) > > (define seq% > (class* object% (seq<%>) > (super-new) > (define/public (get-sequence) > (list 1 2 3)))) > > > (define p (new proc%)) > > (p 1) > this is the proc method of proc% > 1 > > (define s (new seq%)) > > (sequence-for-each displayln s) > 1 > 2 > 3 > > On Oct 2, 2014, at 6:21 PM, Matthew Butterick <m...@mbtype.com> wrote: > > What's the best approach to: > > + defining a class whose instances can be used as procedures? > > (define ci (new proc-class%)) > (ci arg arg2 ... ) > > + ... whose instances can be used as lists (or at least support direct > iteration?) > > (define li (new listish-class%)) > (for-each displayln li) > (map ci li) > > My intuition is "implement a generic interface..." But then it gets hazy. > > > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > > >
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