# Jeffa
   rows => [
      map {{ cols => [ 
         map {
            { data => defined $_ ? encode_entities $_ : ' ' }
         } @$_ 
      ] }} @$row
   ],

# becomes -{diotalevi}->
my ($row, $value);
for $row (@$rows)
  {
    for $value(@$row)
      {
        $value = { data => defined($value)
                           ? encode_entities($value)
                           : ' ' };
      }
    $row = { cols => $row };
  }

# and later
   rows => \@rows