Re^3: loop surprise

[AnomalousMonk]

my $condNum = 0;
for $condNum ( 1 .. 10 ) {
    forceSituation( $conditions[condNum] );
    my $result = measureSituation();
    ...;
    last if $result->is_error();
    ...
}
datalog( value => $condNum, ...);
...

But in that case, why not use a C-style loop

c:\@Work\Perl\monks>perl -wMstrict -le
"use constant N_MAX => 10;
 ;;
 my $nCond;
 ;;
 CONDITION:
 for ($nCond = 1;  $nCond <= N_MAX;  ++$nCond) {
   print $nCond;
   last CONDITION if $nCond >= 3;
   }
 ;;
 print qq{only made it to condition $nCond} if $nCond < N_MAX;
"
1
2
3
only made it to condition 3

(as suggested here)?

[pryrt]

++. I do not deny that there are multiple of fully-functional ways around the issue, and seeing so many of the TIMTOWTDI is one of the many things that draws me to PM, even though the vast bulk of my programming is not in Perl. I was pointing this out as a reasonable circumstance in which one might expect the loop variable to persist. And, like morgon expressed, it is counter-intuitive to me that my $nCond; for $nCond (1 .. 10) and my $nCond; for($nCond=1; $nCond<=10; ++$nCond) would behave differently w/r/t localization of $nCond. But every language has it's own unique character, and that's fine.

If I needed this construct in Perl, I would have eventually settled either on my alternative or this more c-like one... But likely my own alternative: over the last couple years of regularly participating here, my mindset has changed from c-like for-loops to perlish ones, so the c-for idiom is no longer my first (or often even second) choice. And, once I was reminded of the auto-localization in foreach(), I probably would have assumed auto-localization in for(;;), and wouldn't've even tried it.

[choroba]

> it is counter-intuitive to me that my $nCond; for $nCond (1 .. 10) and my $nCond; for($nCond=1; $nCond<=10; ++$nCond) would behave differently w/r/t localization of $nCond

So meditate about it a bit more. In the

for $var (1 .. 10)

case, the $var is in a special position, and you can't use anything else than a scalar variable.

The C-style for loop, on the other hand, is just a while loop in a disguise. All the three constructs in the parentheses are just expressions, i.e. you can use multiple variables there, as in

my ($i, $j);
my $k = 15;
for ($i = 1, $j = 0; $i + $j < $k; $j = ++$i - rand 2) {
    print "$i $j\n";
}

or you can use no variables at all

#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

{
    my $var;
    sub init { $var = 0 }
    sub following { ++$var }
    sub exhausted { $var > 10 }
    sub get { $var }
}

for (init(); ! exhausted(); following()) {
    say get();
}

So, there can't be any implicit localization, as there's nothing in general to localize.

[pryrt]

when you put it that way, it does seem more obvious. Thanks.