# example: building a binary tree from an unsorted file of strings
$_ = <>;
chop;
my $llref;
{ $llref = { data => $_ }; }
while ( <> ) {
    chop;
    Bin( $llref );
}

# on completion there is only $llref defined pointing at a dynamic list element being an anonymous hash with links to other similar list elements.

sub Bin {
    my $llref = shift;
    if ( $_ < $llref -> { data } ) {
        if ( defined ( $llref -> { left } ) ) {
            Bin( $llref -> { left ));
        }
        else {
            $llref -> { left } = { data => $_ };
        }
    elsif( $_ > $llref -> { data } ) {
        if ( defined( $llref -> { right } ) ) {
            Bin( $llref -> { right ));
        }
        else {
            $llref -> { right } = { data => $_ };
        }
    }
}