sub merge {
  my ($pre,$cur,$nex, $mindist) = @_;
  # here write your logic for merging either cur+pre or cur+nex or no merging at all given mindist
  my $decicion_to_merge = ...
  if( $decicion_to_merge == 1 ){ ... merge the intervals ... }
}

##</code><code>##

sub     get_sorted_intervals_as_array {
        my $atree = shift;
        my @ret = ();
        $atree->traverse(
                # specify a func to be run on every node as returned b
+y traverse()
                sub {
                        my $anode = $_[0];
                        print "traverse() : ".$anode->{interval}." => 
+".$anode->str()."\n";
                        push(@ret, $anode);
                }
        );
        return @ret
}

##</code><code>##

my @ints = get_sorted_intervals_as_array($tree);
for($i=1;$i<scalar(@ints)-1;$i++){
   $pre = $ints[$i-1];
   $cur = $ints[$i];
   $nex = $ints[$i+1];
   merge($pre, $cur, $nex, 1234); # 1234 user-specified distance
}

##</code><code>##

my %Interval  = (
   'chromosome' => 'Chr1',
   'from' => 1000,
   'to' => 4000,
    # to represent A1 (?):
   'type' => 'A',
   'id' => 1
);

##</code><code>##

sub can_merge {
  my ($i1, $i2) = @_;
  return $i1->{'type'} ne $2->{'type'}
}
sub merge {
  my ($i1, $i2, $distance) = @_;
  my $newi = {};
  if( $distance ... ){ return undef } # no merge happened because distance etc.
  if( ! can_merge($i1, $i2) ){ return undef } # no merge, types incompatible.
  $newi->{from} = List::Util::min($i1->{from}, $i2->{from});
  $newi->{to} = List::Util::max($i1->{to}, $i2->{to});
  ...
  return $newi # return the new interval representing the merge
}