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*To*: scheme@mc.lcs.mit.edu*Subject*: Re: Efficiency of Y (Was: Limitation with lambda)*From*: mike@arizona.edu (Mike Coffin)*Date*: Tue ,15 Nov 88 12:51:50 EDT*Organization*: U of Arizona CS Dept, Tucson*References*: <8811142229.AA01756@duchamps.ads.com>*Sender*: scheme-request@mc.lcs.mit.edu

From article <8811142229.AA01756@duchamps.ads.com> (Bob Riemenschneider): > Here's a simple experiment you can perform using your favorite Scheme. [three definitions of a factorial function omitted: one iterative, one recursive, and one using the Y combinator] > 3. Compute the factorial of a number using each of the three procedures, > timing the results. Make the number large enough so that you can get > a reasonably accurate timing. (I found 100 worked well for MacScheme, > and 1000 for T on my Sun 3.) > > I found performance of the three to be identical, leading me to believe that, > given current Scheme compiler technology, there's no reason to avoid using Y. I tried this using T. When I performed the experiment as stated, I indeed got identical times for the three definitions: > (time (factorial-loop 100)) virtual time = 0.36 seconds > (time (factorial-rec 100)) virtual time = 0.36 seconds > (time (factorial-lfp 100)) virtual time = 0.36 seconds However, when I instead calculated the factorial of a small number many times, there was a huge difference --- more than a factor of 10 --- between the times: > (time (factorial-loop 10) 1000) virtual time = 0.18 seconds > (time (factorial-rec 10) 1000) virtual time = 0.2 seconds > (time (factorial-lfp 10) 1000) virtual time = 2.58 seconds I think the benchmark, as originally stated, mostly measures the speed of longnum arithmetic, and not the efficiency of the various contol constructs. -- Mike Coffin mike@arizona.edu Univ. of Ariz. Dept. of Comp. Sci. {allegra,cmcl2}!arizona!mike Tucson, AZ 85721 (602)621-2858

**References**:**Efficiency of Y (Was: Limitation with lambda)***From:*zodiac!DUCHAMPS.ADS.COM!rar@ames.arpa (Bob Riemenschneider)

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