Good $localtime honoured monks

I am having a little bother getting a hash slice from an anonymous hash to which I only have a reference. Without further ado some code

#!/usr/bin/perl -l
# this works OK
my @l=qw(this is);
my %e=qw( this 7 is 6 then 9);
print $e{is};
print join "+", @e{@l}
# output
6
7+6

#!/usr/bin/perl
# yet all my attempts to get this working failed
# I tried @{$r->{@l}} @{$r->{@l}} and many more I forget
my @l=qw(this is);
my $r={qw( this 7 is 6 then 9)};
print $r->{is};
print join "+", @{$r->{@l}}
# output
6

# just a blank line above.
[download]

What arcane combination of line noise like sigils will bring me enlightenment ?

Cheers,
R.