I don't believe you can set the value of 'p' here in one call:

$ds->p([ "hey", "you" ]);    # Wrong

$ds->p(0, "hey");            # Sets element 0 and
$ds->p(1, "you");            # Sets element 1; OR:

$ds = new DiscourseSegment ( p => [ "hey", "you" ] );
                             # Sets both at object creation time
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Note that I'm only saying it's wrong because it doesn't seem to be working for me either. The documentation for Class::Struct never seems to indicate that you can set @ types as you're attempting, though I would agree it is a logical way to do it. The docs only mention the two methods I describe above.