sub gen_each_iter(\%) {
   my ($hash) = @_;
   my @keys = keys(%$hash);
   return sub {
      return if not @keys;
      my $key = shift(@keys);
      return wantarray ? ($key, $hash->{$key}) : $key;
   };
};

my $each = gen_each_iter(%foo);

while (my ($key, $val) = $each->()) {
   ...
}

##</code><code>##

my @keys = keys(%foo);

my $each = sub {
   return if not @keys;
   my $key = shift(@keys);
   return ($key, $foo{$key});
};

while (my ($key, $val) = $each->()) {
   ...
}