Re: counting backward

Because the range operator is defined as low .. high and as 10 is higher than 0, it does nothing.

There are a couple of ways of doing what you want:

for my $i ( reverse 0 .. 10 ) { print $i }
Which is okay for small ranges; but creates a huge list for large ones.
for my $i ( -10 .. 0 ) { print -$i }
Which works for any size range without creating a huge list.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

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Re^2: counting backward (optimize foreach reverse low .. high by Anonymous Monk on Mar 02, 2013 at 15:13 UTC
Which is okay for small ranges; but creates a huge list for large ones. :) seems like an easy candidate for optimization , since this is optimized for (reverse @a) is optimized `perl -le " @f = 1 .. 100_000; for(reverse @f ){ $f=$_; $f==$#f and sca +lar<> } " perl -le " @f = 1 .. 100_000; for( @f ){ $f=$_; $f==$#f and scalar<> } + "` [download]	[reply] [d/l]
Re^3: counting backward (optimize foreach reverse low .. high by BrowserUk (Patriarch) on Mar 02, 2013 at 15:29 UTC
But you still had to create a huge array in order to benefit from the optimisation; which kinda negates the purpose. This: `perl -E"@a=1..1e9; for( reverse @a ) { print $_; <> }"` consumes 18GB (that's Gigabytes!) of memory Whereas this: `perl -E"for( -1e9..1 ) { print -$_; <> }"` iterates the same range and consumes only 1.8MB of ram. Four orders of magnitude more memory, or a minus sign. My choice is simple; how about yours? With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l] [select]
Re^4: counting backward (optimize foreach reverse low .. high by Anonymous Monk on Mar 02, 2013 at 15:39 UTC
Four orders of magnitude more memory, or a minus sign. My choice is simple; how about yours? I'll use minus sign until perl5-porter optimizes foreach reverse rangeop Or i'll use for;;;	[reply]
Re^5: counting backward (optimize foreach reverse low .. high by BrowserUk (Patriarch) on Mar 02, 2013 at 16:59 UTC
Re^3: counting backward (optimize foreach reverse low .. high by LanX (Saint) on Mar 02, 2013 at 15:24 UTC
AFAIK `for( @f )` is optimized to act like an iterator without expanding and caching the list. But in `for(reverse @f )` there is no `for`-context which helps `reverse` to act differently. I'm to lazy for benchmarks (we had them before), but this was surely not fixed in 5.8.8 Cheers Rolf	[reply] [d/l] [select]
Re^4: counting backward (optimize foreach reverse low .. high by dave_the_m (Monsignor) on Mar 02, 2013 at 15:35 UTC
`for(reverse @f)` has been optimised not to expand the array since 5.10.0. Dave.	[reply] [d/l]
Re^5: counting backward (optimize foreach reverse low .. high by LanX (Saint) on Mar 02, 2013 at 15:52 UTC
Re^6: counting backward (optimize foreach reverse low .. high by dave_the_m (Monsignor) on Mar 02, 2013 at 17:37 UTC
Re^6: counting backward (optimize foreach reverse low .. high by Anonymous Monk on Mar 02, 2013 at 16:24 UTC
Re^5: counting backward (optimize foreach reverse low .. high by ikegami (Patriarch) on Mar 02, 2013 at 20:46 UTC
Re^4: counting backward (optimize foreach reverse low .. high by Anonymous Monk on Mar 02, 2013 at 15:30 UTC
You're wrong	[reply]
Re^5: counting backward (optimize foreach reverse low .. high by LanX (Saint) on Mar 02, 2013 at 15:56 UTC
Re^6: counting backward (optimize foreach reverse low .. high by Anonymous Monk on Mar 02, 2013 at 16:19 UTC
Re^6: counting backward (optimize foreach reverse low .. high by Anonymous Monk on Mar 02, 2013 at 16:21 UTC