use strict;

sub NEXT { $_[0]->() }

sub string_to_char_iter {
    my $string = shift;
    $string = reverse $string;
    sub { chop $string }
}

sub get_all {
   my $iter = shift;
   my (@list,$char);
   push @list,$char while $char = NEXT $iter;
   return @list;
}

my $string = join '', 'a' .. 'z';
my $iter   = string_to_char_iter $string;

print $_,$/ for map uc, get_all($iter);