sub hmap(&@) {
   my $cb = shift;

   my $caller = caller();
   my $kgr = do { no strict 'refs'; \*{$caller.'::k'} };
   my $vgr = do { no strict 'refs'; \*{$caller.'::v'} };
   local *$kgr = \my $k;
   local *$vgr = \my $v;

   for (...) {
      $k = ...;
      $v = ...;
      $cb->();
   }
}

##</code><code>##

... = hmap { our($k,$v); ... } ...;

##</code><code>##

... = hmap { my($k,$v)=@_; ... } ...;

##</code><code>##

package Hash::Map;

use Exporter qw( import );
our @EXPORT = qw( $k $v hmap hgrep );

sub hmap(&@)  { ... }
sub hgrep(&@) { ... }

1;