On 15/10/12 22:44, Alan Malloy wrote:
On Oct 15, 1:07 pm, "Jim - FooBar();" <jimpil1...@gmail.com> wrote:
On 15/10/12 19:42, Ben Smith-Mannschott wrote:
If the distinction I'm trying to make is not clear to you, I'd suggest
having a look athttp://www.infoq.com/presentations/Clojure-Macros (It
does a good job exploring these kinds of distinctions as it's vital to
have an accurate mental model of how Clojure is evaluated if one
intends to write macros.)
after watching this talk I tried this at a repl:
(defmacro plus
"Perform addition at compile time."
[numbers]
(apply + (eval numbers)))
user=> (time (plus (vec (range 10000))))
"Elapsed time: 0.015635 msecs" ;;WOW
49995000
user=> (time (apply + (vec (range 10000))))
"Elapsed time: 16.732054 msecs" ;;160 times slower
49995000
before jumping to any conclusions (and rushing to change some of my
code) would you say timing is realistic? Is it expected to see such a
dramatic speed increase? To be honest I'm a bit surprised...Regardless
of when the actual calculation will be performed (compile vs run time),
it will eventually be performed. why is at compile time so much faster?
You add the numbers at compile time, and then time how long it takes
to...do nothing to them, at runtime. You are comparing N to zero, not
to some smaller factor of N.
yes but this seems almost unbelievable...i mean for simple numeric
operations this little trick could provide a tremendous speedup. How
come this has not been 'advertised' enough? It is my understanding that
not even Java could go that fast simply because you cannot tap into the
compilation process...is there code that uses this sort of thing for
performance? I'd love to take a peek...
Jim
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