[racket-dev] An Improvement to for/set

for/set sounds and looks more uniform with the rest of the loops, no? 
union you can throw in as a function or for/fold. 


On Feb 17, 2012, at 1:30 PM, J. Ian Johnson wrote:

> I would prefer a simpler for/union:
> 
> (define-syntax (for/union stx)
>  (syntax-case stx ()
>    [(_ clauses . body)
>     #'(for/fold/derived stx ((accum-set (set))) clauses
>         (set-union accum-set (let () . body))]))
> 
> -Ian
> 
> ----- Original Message -----
> From: "Daniel King" <danking at ccs.neu.edu>
> To: "Racket Dev List" <dev at racket-lang.org>
> Sent: Friday, February 17, 2012 1:07:25 PM GMT -05:00 US/Canada Eastern
> Subject: [racket-dev] An Improvement to for/set
> 
> I've noticed myself desiring a for/set that would allow me to
> optionally add zero, one, or more elements to the accumulated set
> during each iteration. Is this something that other people would be
> interested in having in the set library? If so, I can send a pull
> request to the github repo.
> 
> My implementation should be backwards compatible with the old one. I
> also created set-add* because I found myself wanting to add arbitrary
> numbers of elements to sets as well.
> 
> ;; set-add* : [Set X] X ... -> [Set X]
> (define (set-add* s . vs)
>  (for/fold ((s s)) ((v vs))
>    (set-add s v)))
> 
> (define-syntax (for/set stx)
>  (syntax-case stx ()
>    [(_ clauses . body)
>     #'(for/fold/derived stx ((accum-set (set))) clauses
>                         (call-with-values (lambda () . body)
>                           (curry set-add* accum-set)))]))
> 
> Examples:
> 
>> (for/set ((x '(1 2 3 4 5)))
>  (sqr x))
> (set 1 4 9 16 25)
> 
>> (for/set ((x '(1 2 3 4 5)))
>    (if (odd? x) x (values)))
> (set 1 3 5)
> 
> 
> -- 
> Dan King
> College of Computer and Information Science
> Northeastern University
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