Re: [racket-users] Implementing a lazy for/stream using for/fold/derived and delimited control
On 20/05/2015 04:24, Alexis King wrote: I'm trying to implement a for/stream loop using for/fold/derived that will return a lazy stream, as would be expected. One way to do this is by using delimited control, which is what I'm currently trying. If there's an easier way, let me know, but I'd still like to figure this out as a pedagogical exercise. If I understand correctly what you are trying to do, the simplest solution seems to be a generator. = #lang racket (require racket/generator) (define result-stream (in-generator (for ([i (in-naturals 10)]) (yield i (for ([n result-stream]) (printf ~s\n n)) = This example is a bit pointless because result-stream could just as well be replaced by (in-naturals 10), but I hope it is clear how this could be generalized to a meaningful application. I use this a lot, to the point of considering defining something like for/sequence to have nicer syntax for this. Konrad. -- 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 racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [racket-users] Implementing a lazy for/stream using for/fold/derived and delimited control
I've never particularly loved racket/generator's interface, but you're right that it could be a useful base for this sort of abstraction. I do explicitly want a stream, but I could use in-generator in tandem with sequence-stream to get that. That said, I would still be interested in figuring out how to roll it myself using a solution similar to what I proposed for learning purposes. On May 19, 2015, at 23:11, Konrad Hinsen konrad.hin...@fastmail.net wrote: On 20/05/2015 04:24, Alexis King wrote: I'm trying to implement a for/stream loop using for/fold/derived that will return a lazy stream, as would be expected. One way to do this is by using delimited control, which is what I'm currently trying. If there's an easier way, let me know, but I'd still like to figure this out as a pedagogical exercise. If I understand correctly what you are trying to do, the simplest solution seems to be a generator. = #lang racket (require racket/generator) (define result-stream (in-generator (for ([i (in-naturals 10)]) (yield i (for ([n result-stream]) (printf ~s\n n)) = This example is a bit pointless because result-stream could just as well be replaced by (in-naturals 10), but I hope it is clear how this could be generalized to a meaningful application. I use this a lot, to the point of considering defining something like for/sequence to have nicer syntax for this. Konrad. -- 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 racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[racket-users] Implementing a lazy for/stream using for/fold/derived and delimited control
I'm trying to implement a for/stream loop using for/fold/derived that will return a lazy stream, as would be expected. One way to do this is by using delimited control, which is what I'm currently trying. If there's an easier way, let me know, but I'd still like to figure this out as a pedagogical exercise. Right now, I'm just trying to play with for/fold and some control operators to get a feel for how a solution should work. Using racket/control, I've managed to get this working snippet: (define result-stream (let () (define (stream-loop element continue) (stream-cons element (call-with-values (thunk (call/prompt continue)) stream-loop))) (call-with-values (thunk (prompt (for/fold () ([i (in-naturals)]) (let/cc continue (abort i continue) stream-loop))) This will create an infinite, lazy stream bound to ‘result-stream’ containing all the natural numbers. It works, which is cool, but it also seems pretty overcomplicated. Is there a better approach to this sort of thing that I'm missing? My intuition for working with control operators isn't the best, so I wouldn't be surprised if I was overlooking something. Thanks, Alexis -- 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 racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
