[racket-dev] for loop singleton optimization

From: J. Ian Johnson (ianj at ccs.neu.edu)
Date: Wed Nov 28 13:24:12 EST 2012

Cool. I submitted a pull request with this change since it's always an improvement.
----- Original Message -----
From: "Matthew Flatt" <mflatt at cs.utah.edu>
To: "J. Ian Johnson" <ianj at ccs.neu.edu>
Cc: "dev" <dev at racket-lang.org>
Sent: Wednesday, November 28, 2012 12:58:09 PM GMT -05:00 US/Canada Eastern
Subject: Re: [racket-dev] for loop singleton optimization

I think that would be an ad hoc optimization in each `in-'. For example,

(define-sequence-syntax *in-set
  (lambda () #'in-set)
  (lambda (stx)
    (syntax-case stx ()
      [[(id) (_ st)]

in `racket/set' could change to

(define-sequence-syntax *in-set
  (lambda () #'in-set)
  (lambda (stx)
    (syntax-case stx (set)
      [[(id) (_ (set v))]
       #`[(id) (in-value v)]]
      [[(id) (_ st)]

At Wed, 28 Nov 2012 12:50:49 -0500 (EST), "J. Ian Johnson" wrote:
> It would be great to optimize singletons out of comprehensions, since I (and 
> probably others) have macros that expand into singleton constructors that are 
> much better suited to just be a rebinding.
> > (time (for ([n (in-range 1 1000000)]) (for ([k (in-set (set n))]) (random 
> k))))
> cpu time: 340 real time: 338 gc time: 16
> > (time (for ([n (in-range 1 1000000)]) (for ([k (in-value n)]) (random k))))
> cpu time: 120 real time: 118 gc time: 0
> Is this easily added to for.rkt?
> -Ian
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