How many loops are there in Perl?

shajiindia has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: How many loops are there in Perl? by tobyink (Canon) on Jan 31, 2012 at 07:21 UTC
Dunno... does this count? `my ($from, $to) = (1, 3); my $x; $x = sub { my $i = shift; print "Inside recursive sub!\n"; $x->(++$i) if $i < $to; } and $x->($from);` [download] TIMT7WTDI	[reply] [d/l]
Re: How many loops are there in Perl? by JavaFan (Canon) on Jan 31, 2012 at 07:29 UTC
`$i = 10;L: print "Hello"; goto L if --$_i; map {print "Hello"} 1 .. 10; grep {print "Hello"} 1 .. 10; $_ = "abcdefghij"; s/./@{[print "Hello"]}/g; sub foo { print "Hello"; foo($_[0]-1) if $_[0] > 0; } foo(10);` [download]	[reply] [d/l]
Re^2: How many loops are there in Perl? by tobyink (Canon) on Jan 31, 2012 at 08:23 UTC
In the spirit of your `map` and `grep` examples, here's one using `sort`... `perl -E'join("\|", sort {do{say "Inside sort loop"} and $a <=> $b} 3,1, +2)'` [download] Works in 5.10.1, but the Perl sorting algorithm has been known to change from version to version. Note that the `join` does seem to be needed to avoid Perl optimizing away the `sort`.	[reply] [d/l] [select]
Re: How many loops are there in Perl? by repellent (Priest) on Jan 31, 2012 at 08:32 UTC
`[1 .. 5] ~~ sub { say "Inside loop $_[0]?" }; # Perl 5.10.1+` [download]	[reply] [d/l]
Re^2: How many loops are there in Perl? by davido (Cardinal) on Jan 31, 2012 at 18:51 UTC
That's one for the obfu-toolkit. I'm surprised we haven't seen abuse of the regex engine and `(?{...})` blocks. Dave	[reply] [d/l]
Re^3: How many loops are there in Perl? by LanX (Saint) on Feb 01, 2012 at 23:04 UTC
as you wish :) `DB<72> (" "x10) =~ m/ (?{print $x++})/g => (" ", " ", " ", " ", " ", " ", " ", " ", " ", " ") 0123456789` [download] I'm surprised nobody tried `s///e` Cheers Rolf update: `DB<20> $_=" "x10; s/ /print $x++/ge => 10 0123456789` [download]	[reply] [d/l] [select]
Re: How many loops are there in Perl? by Anonymous Monk on Jan 31, 2012 at 06:45 UTC
Am I right? The question is vague. I suppose the naked-block isn't a loop, at least not without a label and goto	[reply]
Re^2: How many loops are there in Perl? by davido (Cardinal) on Jan 31, 2012 at 07:11 UTC
Naked blocks can be loops with no need for goto or labels: `my $i = 0; { redo if $i++ < 10; }` [download] But as worded, the question is difficult to answer; it's hard to know what the person asking is really after and what he or she has or hasn't considered. Dave	[reply] [d/l]
Re^2: How many loops are there in Perl? by AnomalousMonk (Archbishop) on Jan 31, 2012 at 07:03 UTC
... the naked-block isn't a loop ... without a label and goto[.] Or at least a (possibly conditional) redo (see also Loop Control): `perl -wMstrict -le "my $i = 1; { print qq{in naked loop $i}; redo if $i++ < 3; } " in naked loop 1 in naked loop 2 in naked loop 3` [download]	[reply] [d/l]
Re^3: How many loops are there in Perl? by adamcrussell (Hermit) on Jan 31, 2012 at 22:14 UTC
I have always thought redo was cool. At first glance it doesn't look anything like a goto because it is usually used with bare blocks. The code below has redo going to the start of the nearest enclosing block. `{ print "Enter a number 0-9\n"; $number=<STDIN>; chomp($number); unless(length($number) == 1 && $number =~ /[0-9]/){ print "C'mon, man! give me a number 0-9!\n"; redo; } }` [download] However, redo can take an argument (a block label) which makes it look much more goto-ish and less like elegant Perl. For example, we could redo (pun intended!) the example like this: `GET_NUMBER:{ print "Enter a number 0-9\n"; $number=<STDIN>; chomp($number); unless(length($number) == 1 && $number =~ /[0-9]/){ print "C'mon, man! give me a number 0-9!\n"; redo GET_NUMBER; } }` [download] The biggest difference between redo and a pure goto is that redo must go to an enclosing block label whereas goto goes to any label. This is still a valid redo: `my $number; PROMPT_FOR_NUMBER:{ print "Enter a number 0-9\n"; GET_NUMBER:{ $number=<STDIN>; chomp($number); unless(length($number) ==1 && $number =~ /[0-9]/){ print "You don't want to give me one number ?\n"; redo PROMPT_FOR_NUMBER; } } }` [download] <jc> Why do people persist in asking me stupid questions? <Petruchio> <insert mutually recursive response> --an exchange from #perlmonks on irc.slashnet.org(2 March 2009 1345 EST)	[reply] [d/l] [select]
Re^2: How many loops are there in Perl? by Anonymous Monk on Jan 31, 2012 at 06:49 UTC
Also, by OPs criteria, `do { } for` and `do { } foreach` (with or without the do block) could be considered four more loops	[reply] [d/l] [select]
Re^2: How many loops are there in Perl? by bimleshsharma (Beadle) on Jan 31, 2012 at 09:59 UTC
Actualy question is not vague but naked braces is not a loop. SO whatever you have said 6 loops that is fine.	[reply]
Re^3: How many loops are there in Perl? by Anonymous Monk on Feb 02, 2012 at 09:37 UTC
Yes, the question as asked is extremely vague, as evidenced by the things offered as loops map/grep/foreach cannot loop forever, they are iterators, but are still considered loops by some `$ perl -le " print for 1 .. INF " Range iterator outside integer range at -e line 1.` [download]	[reply] [d/l]
Re: How many loops are there in Perl? by cursion (Pilgrim) on Jan 31, 2012 at 14:04 UTC
`print something() x10;` [download] EDIT: On second thought (see reply to this) .. this only applies to a very loose definition (aka incorrect) of a loop.	[reply] [d/l]
Re^2: How many loops are there in Perl? by LanX (Saint) on Feb 01, 2012 at 22:47 UTC
not a loop because something() is only executed once and not 10 times. Cheers Rolf	[reply]
Re: How many loops are there in Perl? by jdrago999 (Pilgrim) on Jan 31, 2012 at 18:30 UTC
How about with Perl6? I'd like to see how a hyperoperator could be used to simulate a loop.	[reply]
Re: How many loops are there in Perl? by rir (Vicar) on Feb 01, 2012 at 21:50 UTC
One or two, depends on whether you're willing to accept it capitalized. Cursive is not considered. Perl6 goes one better. Be well, rir	[reply]


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