sub flatten_list {
   my ($rv, $p) = @_;
   @$rv = ();
   while ($p) {
      unshift @$rv, $p->[1];
      $p = $p->[0];
   }
}

our @matches;
local *matches;
/
   $text
   (?:
      \s
      (\w+)
      (?{ [ $^R, $1 ] })
   )+
   (?{ flatten_list \@matches, $^R })
/x;