$type morgon2.pl
use strict;
use warnings;
use List::MoreUtils 'indexes';
my @array=(1,2);

my $i1 = indexes { $array[$_] == 1 } (0..$#array);
my $i2 = indexes { $array[$_] == 2 } (0..$#array);
my $i3 = indexes { $array[$_] == 3 } (0..$#array);

print "<$i1> <$i2> <$i3>\n";


$perl morgon2.pl
Use of uninitialized value $i3 in concatenation (.) or string at morgon2.pl line
 10.
<0> <1> <>