# Partition a string into paragraphs based on a 
# pattern which matches the beginning of a paragraph.
sub partition_para_beg {
   my ($pat, $str) = @_;
   $str = $_ unless defined $str;
   if ("" =~ /$pat/) {
      require Carp;
      Carp::croak("invalid pattern matches empty string: \"$pat\"\n");
   }
   split /(?=$pat)/;
}

# Partition a string into paragraphs based on a 
# pattern which matches the end of a paragraph.
sub partition_para_end {
   my ($pat, $str) = @_;
   $str = $_ unless defined $str;
   if ("" =~ /$pat/) {
      require Carp;
      Carp::croak("invalid pattern matches empty string: \"$pat\"\n");
   }
   return $str =~ /(.*?(?:$pat)|.+)/gs;
}