For personal reference.
Not fully tested.

Change:
   stmt_list  : SEP(s?) stmt SET_IN_CODE stmt_list_(s?) SEP(s?)
                { [ $item[2], @{$item[4]} ] }

Change:
   stmt_list_ : seps stmt { $item[2] }

Add:
   seps       : SEP(s)
              | {
                   my $idx  = 1;
                   my $line = $itempos[$idx]{line}{from};
                   my $col  = $itempos[$idx]{column}{from};
                   warn("$line,$col: Expecting ';'.\n");
                   REJECT
                }

Remove:
    sep