You need to set $Data::Dumper::Deparse to a true value.

use Data::Dumper;
$Data::Dumper::Deparse = 1;
$foo = sub {return []};
$bar = {arefpromise => $foo};
$d = Data::Dumper->new([$bar]);
print "foo is a coderef $foo returning ".$foo->()."\n";
$d->Seen ({$foo => $foo->()});
print $d->Dump();
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will print

foo is a coderef CODE(0x801734) returning ARRAY(0x801944)
$VAR1 = {
          'arefpromise' => sub {
                               return [];
                           }
        };
[download]