#! perl -slw
use strict;
use List::Util qw[ reduce ];

my $s = 'this is a test';

reduce{
    print "$a:$b";
    $b;
} split ' ', $s;
print "\n---\n";

my @p;
reduce{
    print "$a:$b";
    push @p, [ 1, 2 ];
    $b;
} split ' ', $s;
print "\n---\n";

my @q;
reduce{
    print "$a:$b";
    push @q, [ $a, 2 ];
    $b;
} split ' ', $s;
print "\n---\n";

my @r;
reduce{
    print "$a:$b";
    push @r, [ $a, $b ];
    $b;
} split ' ', $s;

__END__

c:\test>junk3
this:is
is:a
a:test

---

this:is
is:a
a:test

---

this:is
is:a
a:test

---

this:is
Use of uninitialized value in concatenation (.) or string at c:\test\junk3.pl line 31.
:a
Use of uninitialized value in concatenation (.) or string at c:\test\junk3.pl line 31.
:test