http://www.perlmonks.org?node_id=950892


in reply to How many loops are there in Perl?

Am I right?

The question is vague.

I suppose the naked-block isn't a loop, at least not without a label and goto

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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;
}

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    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

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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

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      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;  
    }
}

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      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;  
    }
}

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      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;
            }
        } 
}

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      <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)
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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
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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.

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      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.

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