why not-DWIMmy-enough infix:<+> is annoying

            when $.lintel_move {
                # RAKUDO: Hoping these explicit int(...) conversions won't be
                #         necessary in the long run.
                my Int $row_1    = int($<coords>[0]<row_number> - 1);
                my Int $row_2    = int($<coords>[1]<row_number> - 1);
                my Int $column_1
                    = int(ord($<coords>[0]<col_letter>) - ord('a'));
                my Int $column_2
                    = int(ord($<coords>[1]<col_letter>) - ord('a'));

                fail $reason if my $reason
                    = self.is-lintel-move-bad($row_1, $row_2,
                                              $column_1, $column_2,
                                              $color);

                my $height   = @!heights[$row_1][$column_1];
                my $row_m    = ($row_1    + $row_2   ) / 2;
                my $column_m = ($column_1 + $column_2) / 2;

                @pieces_to_put = $height, $row_1, $column_1,
                                 $height, $row_m, $column_m,
                                 $height, $row_2, $column_2;
            }