use List::Util qw/reduce/;
# my ($a,$b)=(0,0);
print reduce { $b+=$a } 1..10;

##</code><code>##

use warnings;
use strict;

# my ($a,$b)=(0,0);

use List::MoreUtils qw/pairwise/;
my @a = (1 .. 5);
my @b = (11 .. 15);
my @x = pairwise { $a + $b } @a, @b;   # returns 12, 14, 16, 18, 20

use Data::Dump;
dd \@x; 

##</code><code>##

my ($a,$b)=(0,0);
print sort { $b cmp $a } 1..10;

##</code><code>##

Can't use "my $b" in sort comparison at ... line 2.

##</code><code>##

use warnings;
use strict;

our ($a,$b);

package Tst;

print sort { $b cmp $a } 1..10;

##</code><code>##

Use of uninitialized value $b in string comparison (cmp) at /home/lanx/B/PL/PM/ScopeListUtils.pl line 9.
Use of uninitialized value $a in string comparison (cmp) at /home/lanx/B/PL/PM/ScopeListUtils.pl line 9.
Use of uninitialized value $b in string comparison (cmp) at /home/lanx/B/PL/PM/ScopeListUtils.pl line 9.
Use of uninitialized value $a in string comparison (cmp) at /home/lanx/B/PL/PM/ScopeListUtils.pl line 9.
...