FYI: I do have a sample implementation which works. From the tests:

  $data = {
      foo => 3,
      bar => [ qw/ this that 3 / ],
      3   => undef,
      baz => {
          trois => 3,
          quatre => [ qw/ 1 2 3 4 / ],
      }
  };
  ok $paths = path( $data, 3 ),
    'Fetching paths for matching data should succeed';
  my @expected = sort (
      '{bar}[2]',
      '{baz}{trois}',
      '{baz}{quatre}[2]',
      '{foo}'
  );

  $paths = [ sort @$paths ];
  is_deeply $paths, \@expected,
      '... and we should be able to match complex data structures';

  foreach my $path (@$paths) {
      is eval "\$data->$path", 3,
        '... and each element should have the correct value';
  }
[download]

And the some rough code:

  use Scalar::Util 'reftype';

  my %path = (
      ARRAY => \&_array_path,
      HASH  => \&_hash_path,
  );

  sub path {
      my ( $data, $search ) = @_;
      my $type = reftype $data;
      my $find_paths = $path{$type};
      return $find_paths->( $data, $search );
  }

  sub _array_path {
      my ( $data, $search ) = @_;
      my @paths;
      foreach my $i (0 .. $#$data) {
          my $item = $data->[$i];
          my $type = reftype $item;
          my $current_index = "[$i]";
          if ( !$type && $item eq $search ) {   # XXX
              push @paths => $current_index;
          }
          elsif ( my $find_paths = $path{$type} ) {
              my @current_paths = map { "$current_index$_" }
                  @{ $find_paths->( $item, $search ) };
              push @paths => @current_paths;
          }
      }
      return \@paths;
  }

  sub _hash_path {
      my ( $data, $search ) = @_;
      my @paths;
      foreach my $key (keys %$data) {
          my $item = $data->{$key};
          my $type = reftype $item;
          my $current_key = "{$key}";
          if ( !$type && $item eq $search ) {   # XXX
              push @paths => $current_key;
          }
          elsif ( my $find_paths = $path{$type} ) {
              my @current_paths = map { "$current_key$_" }
                  @{ $find_paths->( $item, $search ) };
              push @paths => @current_paths;
          }
      }
      return \@paths;
  }
[download]

The code itself works fine, but the tests show that using it (the string eval) seems really clumsy. It works fine for what I need, but still looking for a better approach (cleaner and faster).

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