`match-define` seems to be the real source of the speedup for me:
#lang racket
(define (as)
(build-list 1000000 (λ (n) (random 100))))
(define (bs)
(build-list 1000000 (λ (n) (random 100))))
(define (f as bs [acc 0])
(if (or (null? as) (null? bs))
acc
(f (rest as) (rest bs) (+ acc (* (first as) (first bs))))))
(let ([as (as)]
[bs (bs)])
(collect-garbage)
(collect-garbage)
(collect-garbage)
(time (f as bs)))
(define (g as bs)
(let g ([as as]
[bs bs]
[acc 0])
(cond
[(or (null? as) (null? bs))
acc]
[else
(match-define (cons this-a more-as)
as)
(match-define (cons this-b more-bs)
bs)
(g more-as more-bs (+ acc (* this-a this-b)))])))
(let ([as (as)]
[bs (bs)])
(collect-garbage)
(collect-garbage)
(collect-garbage)
(time (g as bs)))
(collect-garbage)
(collect-garbage)
(collect-garbage)
(define (z as bs [acc 0])
(cond
[(or (null? as) (null? bs))
acc]
[else
(match-define (cons this-a more-as)
as)
(match-define (cons this-b more-bs)
bs)
(z more-as more-bs (+ acc (* this-a this-b)))]))
(let ([as (as)]
[bs (bs)])
(collect-garbage)
(collect-garbage)
(collect-garbage)
(time (z as bs)))
; timed at the command line
;cpu time: 242 real time: 241 gc time: 0
;2452993452
;cpu time: 21 real time: 21 gc time: 0
;2450414634
;cpu time: 22 real time: 22 gc time: 0
;2450010495
-Philip
On Thu, Jul 27, 2017 at 8:22 PM, Matthias Felleisen <matth...@ccs.neu.edu>
wrote:
>
> On Jul 27, 2017, at 9:18 PM, Matthew Flatt <mfl...@cs.utah.edu> wrote:
>
> I don't think optional arguments are all that slow.
>
>
>
> This isn’t just Matthew’s opinion. Vincent’s feature-specific profiler
> could not detect a significant impact of optional or keyword arguments.
> (See Compiler Construction paper, London 2014 I think)
>
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