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" <[email protected]> > To: "Racket Dev List" <[email protected]> > 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 > _________________________ > Racket Developers list: > http://lists.racket-lang.org/dev > _________________________ > Racket Developers list: > http://lists.racket-lang.org/dev _________________________ Racket Developers list: http://lists.racket-lang.org/dev
