>perl -wMstrict -MData::Dump -le
"my %mapp;
 my @arr = qw(R T HH M);
 ;;
 $mapp{k} = \@arr;
 my @val = $mapp{k};
 ;;
 dd \%mapp;
 dd \@val;
 ;;
 print join q{,}, @{$mapp{k}};
 ;;
 push @val, 'RBB';
 dd \@val;
 ;;
 $mapp{k} = \@val;
 dd \%mapp;
 ;;
 print join q{,}, @{$mapp{k}};
 print join q{,}, @{ $mapp{k}->[0] }, $mapp{k}->[1];
"
{ k => ["R", "T", "HH", "M"] }

[["R", "T", "HH", "M"]]

R,T,HH,M
[["R", "T", "HH", "M"], "RBB"]

{ k => [["R", "T", "HH", "M"], "RBB"] }

ARRAY(0x1e14b3c),RBB
R,T,HH,M,RBB