sub iter {
    my $vals = \@_;
    my $i = 0;
    sub {
        $i >= @$vals ? do { $i = 0; undef } : $vals->[$i++];
    };
}

sub enumerate_iter {
    local $Data::Dumper::Indent = 0;
    local $Data::Dumper::Terse = 1;
    my ($iter) = @_;
    my $i = 0;
    while (defined($_ = $iter->())) {
        printf "%2d: (%s)\n", $i++, Dumper($_);
    }
    print "\n";
}

enumerate_iter( iter( qw[a b c] ) );
#  0: ('a')
#  1: ('b')
#  2: ('c')