"_" should ignore in match, but compiler tries to capture and fails with "cannot capture "_", variable not defined"

underscore-in-match-fails.pony

be behave() =>
    if _has_food then //heading home
      _current_cell.get_is_home(
        Promise[Bool].>next[None](
          {(is_home: Bool)(ant = recover tag this end) =>
            if is_home then
              ant.access({(ant': Ant ref) =>
                ant'.drop_food()
                ant'.turn(4)})
            else
              _current_cell.query_neighbors_ahead(
                _direction,
                Promise[(CellInfo, CellInfo, CellInfo)].>next[None](
                  {(cells: (CellInfo, CellInfo, CellInfo)) =>
                    match cells
                    | (_, (let ahead_cell: Cell, _, _, None, true), _) =>
                    //TODO better occupancy check, should consult occupant if present
                      ahead_cell.request_move(
                        ant,
                        Promise[Bool].>next[None](
                          {(did_move: Bool) =>
                            did_move} iso))
                    end
                  } iso))
            end} iso))
    end