my %record_seq_handler= (
    'A' => \&unpack_a,
    'B' => \&unpack_B,
    'C' => \&unpack_C,
);

my $handler= $record_seq_handler{ $RECORD_SEQ_ID }
    or die "Unknown record sequence '$RECORD_SEQ_ID'";
$handler->( $lines[$_] );