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
}