next in block in foreach-loop

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

Hello,

I've got a problem with Activeperl Built 631 (Win2k) with a next-statement.

If I execute it like the following:

C:\ce3\bin>perl -w
my @list = qw(0 1 2 3 4 5);
foreach (@list){
  next if $_ == 0;
  print $_, " ";
}
^Z
1 2 3 4 5
[download]

everything works fine.

But if I try the following:

C:\ce3\bin>perl -w
use strict;
my @list = qw(0 1 2 3 4 5);
foreach (@list){
  { 
    next if $_ == 0;
  }
  print $_, " ";
}
^Z
0 1 2 3 4 5
[download]

On the other hand, this works fine:

C:\ce3\bin>perl -w
my @list = qw(0 1 2 3 4 5);
foreach (@list){
  {
    next if $_ == 0;
    print $_, " ";
  }
}
^Z
1 2 3 4 5
[download]

Is this a perl bug, or am I the bug?

The same behaviour happens with Perl 5.005_03 under Solaris.

Best regards,
perl -le "s==*F=e=>y~\*martinF~stronat~=>s~[^\w]~~g=>chop,print"

Comment on next in block in foreach-loop Select or Download Code

Replies are listed 'Best First'.
Re: next in block in foreach-loop by danger (Priest) on Apr 22, 2002 at 16:03 UTC
A bare block is a loop that executes once but obeys loop control statements such as last, next, and redo. Thus, when you next in the bare-block inside your loop, you are next'ing out of the bare-block, not the outer loop.	[reply]
Re: next in block in foreach-loop by erikharrison (Deacon) on Apr 22, 2002 at 16:07 UTC
The problem is an extra set of braces you are using in the second bit of code there. You have a nested bare block inside the foreach, the next breaks out of it, NOT the foreach. `use strict; my @list = qw(0 1 2 3 4 5); foreach (@list){ #opens up the foreach block . . . { #opens up a new block . . . next if $_ == 0; #breaks out of enclosing block } #meaning it breaks to here. print $_, " "; #so '0' get's printed anyway } #ends the foreach` [download] Be careful about these extra blocks by using labels and explicitly breaking with them. Labels are goood practice for complicated loop structures anyway, for clarity's sake. Cheers, Erik	[reply] [d/l]
Re: next in block in foreach-loop by broquaint (Abbot) on Apr 22, 2002 at 16:04 UTC
You can use loop control functions within blocks (be they bare or named) e.g `{ print "enter option here: "; chomp(my $answer = <STDIN>); redo if $answer ne "quit"; }` [download] So the your example code is behaving as expected. HTH broquaint	[reply] [d/l]
Re: next in block in foreach-loop by particle (Vicar) on Apr 22, 2002 at 16:32 UTC
broquaint and erikharrison both mentioned labels, but neither provided an example. here's one: `my @list = qw(0 1 2 3 4 5); LOOP: foreach (@list){ { next LOOP if $_ == 0; print $_, " "; } }` [download] this should behave as expected. ~Particle ;Þ	[reply] [d/l]


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