BrowserUk: Your implementation of  hmap and  hgrep is a little tricky, but I certainly wouldn't describe it as 'quite obfuscated'! However...

sub hmap (&\%) {
    my( $code, $href ) = @_;
    map{
        local @_;
        $code->( @_ = each %$href )
    } 1 .. keys %$href;
}
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In the code above, I don't see the point of local-izing  @_ and then assigning  each to it. Passing the return of  each %$href 'directly' to the coderef seems to work just as well.

>perl -wMstrict -MData::Dump -le
"sub hmap (&\%) {
     my( $code, $href ) = @_;
     map{
         $code->(each %$href)
     } 1 .. keys %$href;
 }
 ;;
 my %h = 'a'..'z';
 ;;
 print join ' ', hmap { qq{$_[0] => $_[1]} } %h;
 ;;
 my %orig = (
     cat       => 22,
     dog       => 23,
     category  => 66,
     catalyst  => 77,
     cataclysm => 88,
     dogma     => 89,
     dogstar   => 92,
 );
 my %h2 = hmap { $_[0], $_[1] + $_[1] } %orig;
 dd \%h2;
"
w => x e => f a => b m => n s => t y => z u => v c => d k => l q => r 
+g => h i => j o => p
{
  cat => 44,
  cataclysm => 176,
  catalyst => 154,
  category => 132,
  dog => 46,
  dogma => 178,
  dogstar => 184,
}
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