[racket-dev] Surprising behavior of for/fold. Bug?

This is syntactically brittle design. Argh. 




On Jul 29, 2014, at 4:50 PM, "J. Ian Johnson" <ianj at ccs.neu.edu> wrote:

> I forgot that aspect of #:when and #:unless. Sorry for the noise.
> -Ian
> ----- Original Message -----
> From: "Sam Tobin-Hochstadt" <samth at cs.indiana.edu>
> To: "J. Ian Johnson" <ianj at ccs.neu.edu>
> Cc: "dev" <dev at racket-lang.org>
> Sent: Tuesday, July 29, 2014 4:46:49 PM GMT -05:00 US/Canada Eastern
> Subject: Re: [racket-dev] Surprising behavior of for/fold. Bug?
> 
> `#:when` and `#:unless` introduce nesting, a la `for/fold*`. So yes,
> you should expect this.
> 
> Sam
> 
> On Tue, Jul 29, 2014 at 1:23 PM, J. Ian Johnson <ianj at ccs.neu.edu> wrote:
>> This will eat all your memory,
>> 
>> (for/list ([x '(0 1 2 3 4 5 6)]
>>           #:unless (= x 4)
>>           [i (in-naturals)])
>>  x)
>> 
>> and this won't.
>> 
>> (for/list ([x '(0 1 2 3 4 5 6)]
>>           [i (in-naturals)]
>>           #:unless (= x 4))
>>  x)
>> 
>> Should we expect this behavior? I was really surprised by this.
>> -Ian
>> _________________________
>>  Racket Developers list:
>>  http://lists.racket-lang.org/dev
> _________________________
>  Racket Developers list:
>  http://lists.racket-lang.org/dev