Provided by: liblist-compare-perl_0.55-2_all bug

NAME

       List::Compare - Compare elements of two or more lists

VERSION

       This document refers to version 0.55 of List::Compare.  This version was released August
       16 2020.

SYNOPSIS

       The bare essentials:

           @Llist = qw(abel abel baker camera delta edward fargo golfer);
           @Rlist = qw(baker camera delta delta edward fargo golfer hilton);

           $lc = List::Compare->new(\@Llist, \@Rlist);

           @intersection = $lc->get_intersection;
           @union = $lc->get_union;

       ... and so forth.

DISCUSSION: Modes and Methods

   Regular Case:  Compare Two Lists
       •   Constructor:  "new()"

           Create a List::Compare object.  Put the two lists into arrays (named or anonymous) and
           pass references to the arrays to the constructor.

               @Llist = qw(abel abel baker camera delta edward fargo golfer);
               @Rlist = qw(baker camera delta delta edward fargo golfer hilton);

               $lc = List::Compare->new(\@Llist, \@Rlist);

           By default, List::Compare's methods return lists which are sorted using Perl's default
           "sort" mode:  ASCII-betical sorting.  Should you not need to have these lists sorted,
           you may achieve a speed boost by constructing the List::Compare object with the
           unsorted option:

               $lc = List::Compare->new('-u', \@Llist, \@Rlist);

           or

               $lc = List::Compare->new('--unsorted', \@Llist, \@Rlist);

       •   Alternative Constructor

           If you prefer a more explicit delineation of the types of arguments passed to a
           function, you may use this 'single hashref' kind of constructor to build a
           List::Compare object:

               $lc = List::Compare->new( { lists => [\@Llist, \@Rlist] } );

           or

               $lc = List::Compare->new( {
                   lists    => [\@Llist, \@Rlist],
                   unsorted => 1,
               } );

       •   "get_intersection()"

           Get those items which appear at least once in both lists (their intersection).

               @intersection = $lc->get_intersection;

       •   "get_union()"

           Get those items which appear at least once in either list (their union).

               @union = $lc->get_union;

       •   "get_unique()"

           Get those items which appear (at least once) only in the first list.

               @Lonly = $lc->get_unique;
               @Lonly = $lc->get_Lonly;    # alias

       •   "get_complement()"

           Get those items which appear (at least once) only in the second list.

               @Ronly = $lc->get_complement;
               @Ronly = $lc->get_Ronly;            # alias

       •   "get_symmetric_difference()"

           Get those items which appear at least once in either the first or the second list, but
           not both.

               @LorRonly = $lc->get_symmetric_difference;
               @LorRonly = $lc->get_symdiff;       # alias
               @LorRonly = $lc->get_LorRonly;      # alias

       •   "get_bag()"

           Make a bag of all those items in both lists.  The bag differs from the union of the
           two lists in that it holds as many copies of individual elements as appear in the
           original lists.

               @bag = $lc->get_bag;

       •   Return references rather than lists

           An alternative approach to the above methods:  If you do not immediately require an
           array as the return value of the method call, but simply need a reference to an
           (anonymous) array, use one of the following parallel methods:

               $intersection_ref = $lc->get_intersection_ref;
               $union_ref        = $lc->get_union_ref;
               $Lonly_ref        = $lc->get_unique_ref;
               $Lonly_ref        = $lc->get_Lonly_ref;                 # alias
               $Ronly_ref        = $lc->get_complement_ref;
               $Ronly_ref        = $lc->get_Ronly_ref;                 # alias
               $LorRonly_ref     = $lc->get_symmetric_difference_ref;
               $LorRonly_ref     = $lc->get_symdiff_ref;               # alias
               $LorRonly_ref     = $lc->get_LorRonly_ref;              # alias
               $bag_ref          = $lc->get_bag_ref;

       •   "is_LsubsetR()"

           Return a true value if the first argument passed to the constructor ('L' for 'left')
           is a subset of the second argument passed to the constructor ('R' for 'right').

               $LR = $lc->is_LsubsetR;

           Return a true value if R is a subset of L.

               $RL = $lc->is_RsubsetL;

       •   "is_LequivalentR()"

           Return a true value if the two lists passed to the constructor are equivalent, i.e. if
           every element in the left-hand list ('L') appears at least once in the right-hand list
           ('R') and vice versa.

               $eqv = $lc->is_LequivalentR;
               $eqv = $lc->is_LeqvlntR;            # alias

       •   "is_LdisjointR()"

           Return a true value if the two lists passed to the constructor are disjoint, i.e. if
           the two lists have zero elements in common (or, what is the same thing, if their
           intersection is an empty set).

               $disj = $lc->is_LdisjointR;

       •   "print_subset_chart()"

           Pretty-print a chart showing whether one list is a subset of the other.

               $lc->print_subset_chart;

       •   "print_equivalence_chart()"

           Pretty-print a chart showing whether the two lists are equivalent (same elements found
           at least once in both).

               $lc->print_equivalence_chart;

       •   "is_member_which()"

           Determine in which (if any) of the lists passed to the constructor a given string can
           be found.  In list context, return a list of those indices in the constructor's
           argument list corresponding to lists holding the string being tested.

               @memb_arr = $lc->is_member_which('abel');

           In the example above, @memb_arr will be:

               ( 0 )

           because 'abel' is found only in @Al which holds position 0 in the list of arguments
           passed to "new()".

           In scalar context, the return value is the number of lists passed to the constructor
           in which a given string is found.

           As with other List::Compare methods which return a list, you may wish the above method
           returned a (scalar) reference to an array holding the list:

               $memb_arr_ref = $lc->is_member_which_ref('baker');

           In the example above, $memb_arr_ref will be:

               [ 0, 1 ]

           because 'baker' is found in @Llist and @Rlist, which hold positions 0 and 1,
           respectively, in the list of arguments passed to "new()".

           Note:  methods "is_member_which()" and "is_member_which_ref" test only one string at a
           time and hence take only one argument.  To test more than one string at a time see the
           next method, "are_members_which()".

       •   "are_members_which()"

           Determine in which (if any) of the lists passed to the constructor one or more given
           strings can be found.  The strings to be tested are placed in an array (named or
           anonymous); a reference to that array is passed to the method.

               $memb_hash_ref =
                   $lc->are_members_which([ qw| abel baker fargo hilton zebra | ]);

           Note:  In versions of List::Compare prior to 0.25 (April 2004), the strings to be
           tested could be passed as a flat list.  This is no longer possible; the argument must
           now be a reference to an array.

           The return value is a reference to a hash of arrays.  The key for each element in this
           hash is the string being tested.  Each element's value is a reference to an anonymous
           array whose elements are those indices in the constructor's argument list
           corresponding to lists holding the strings being tested.  In the examples above,
           $memb_hash_ref will be:

               {
                    abel     => [ 0    ],
                    baker    => [ 0, 1 ],
                    fargo    => [ 0, 1 ],
                    hilton   => [    1 ],
                    zebra    => [      ],
               };

           Note:  "are_members_which()" can take more than one argument; "is_member_which()" and
           "is_member_which_ref()" each take only one argument.  Unlike those two methods,
           "are_members_which()" returns a hash reference.

       •   "is_member_any()"

           Determine whether a given string can be found in any of the lists passed as arguments
           to the constructor.  Return 1 if a specified string can be found in any of the lists
           and 0 if not.

               $found = $lc->is_member_any('abel');

           In the example above, $found will be 1 because 'abel' is found in one or more of the
           lists passed as arguments to "new()".

       •   "are_members_any()"

           Determine whether a specified string or strings can be found in any of the lists
           passed as arguments to the constructor.  The strings to be tested are placed in an
           array (named or anonymous); a reference to that array is passed to "are_members_any".

               $memb_hash_ref = $lc->are_members_any([ qw| abel baker fargo hilton zebra | ]);

           Note:  In versions of List::Compare prior to 0.25 (April 2004), the strings to be
           tested could be passed as a flat list.  This is no longer possible; the argument must
           now be a reference to an array.

           The return value is a reference to a hash where an element's key is the string being
           tested and the element's value is 1 if the string can be found in any of the lists and
           0 if not.  In the examples above, $memb_hash_ref will be:

               {
                    abel     => 1,
                    baker    => 1,
                    fargo    => 1,
                    hilton   => 1,
                    zebra    => 0,
               };

           "zebra"'s value is 0 because "zebra" is not found in either of the lists passed as
           arguments to "new()".

       •   "get_version()"

           Return current List::Compare version number.

               $vers = $lc->get_version;

   Accelerated Case:  When User Only Wants a Single Comparison
       •   Constructor "new()"

           If you are certain that you will only want the results of a single comparison,
           computation may be accelerated by passing '-a' or "'--accelerated" as the first
           argument to the constructor.

               @Llist = qw(abel abel baker camera delta edward fargo golfer);
               @Rlist = qw(baker camera delta delta edward fargo golfer hilton);

               $lca = List::Compare->new('-a', \@Llist, \@Rlist);

           or

               $lca = List::Compare->new('--accelerated', \@Llist, \@Rlist);

           As with List::Compare's Regular case, should you not need to have a sorted list
           returned by an accelerated List::Compare method, you may achieve a speed boost by
           constructing the accelerated List::Compare object with the unsorted option:

               $lca = List::Compare->new('-u', '-a', \@Llist, \@Rlist);

           or

               $lca = List::Compare->new('--unsorted', '--accelerated', \@Llist, \@Rlist);

       •   Alternative Constructor

           You may use the 'single hashref' constructor format to build a List::Compare object
           calling for the Accelerated mode:

               $lca = List::Compare->new( {
                   lists    => [\@Llist, \@Rlist],
                   accelerated => 1,
               } );

           or

               $lca = List::Compare->new( {
                   lists    => [\@Llist, \@Rlist],
                   accelerated => 1,
                   unsorted => 1,
               } );

       •   Methods

           All the comparison methods available in the Regular case are available to you in the
           Accelerated case as well.

               @intersection     = $lca->get_intersection;
               @union            = $lca->get_union;
               @Lonly            = $lca->get_unique;
               @Ronly            = $lca->get_complement;
               @LorRonly         = $lca->get_symmetric_difference;
               @bag              = $lca->get_bag;
               $intersection_ref = $lca->get_intersection_ref;
               $union_ref        = $lca->get_union_ref;
               $Lonly_ref        = $lca->get_unique_ref;
               $Ronly_ref        = $lca->get_complement_ref;
               $LorRonly_ref     = $lca->get_symmetric_difference_ref;
               $bag_ref          = $lca->get_bag_ref;
               $LR               = $lca->is_LsubsetR;
               $RL               = $lca->is_RsubsetL;
               $eqv              = $lca->is_LequivalentR;
               $disj             = $lca->is_LdisjointR;
                                   $lca->print_subset_chart;
                                   $lca->print_equivalence_chart;
               @memb_arr         = $lca->is_member_which('abel');
               $memb_arr_ref     = $lca->is_member_which_ref('baker');
               $memb_hash_ref    = $lca->are_members_which(
                                       [ qw| abel baker fargo hilton zebra | ]);
               $found            = $lca->is_member_any('abel');
               $memb_hash_ref    = $lca->are_members_any(
                                       [ qw| abel baker fargo hilton zebra | ]);
               $vers             = $lca->get_version;

           All the aliases for methods available in the Regular case are available to you in the
           Accelerated case as well.

   Multiple Case:  Compare Three or More Lists
       •   Constructor "new()"

           Create a List::Compare object.  Put each list into an array and pass references to the
           arrays to the constructor.

               @Al     = qw(abel abel baker camera delta edward fargo golfer);
               @Bob    = qw(baker camera delta delta edward fargo golfer hilton);
               @Carmen = qw(fargo golfer hilton icon icon jerky kappa);
               @Don    = qw(fargo icon jerky);
               @Ed     = qw(fargo icon icon jerky);

               $lcm = List::Compare->new(\@Al, \@Bob, \@Carmen, \@Don, \@Ed);

           As with List::Compare's Regular case, should you not need to have a sorted list
           returned by a List::Compare method, you may achieve a speed boost by constructing the
           object with the unsorted option:

               $lcm = List::Compare->new('-u', \@Al, \@Bob, \@Carmen, \@Don, \@Ed);

           or

               $lcm = List::Compare->new('--unsorted', \@Al, \@Bob, \@Carmen, \@Don, \@Ed);

       •   Alternative Constructor

           You may use the 'single hashref' constructor format to build a List::Compare object to
           process three or more lists at once:

               $lcm = List::Compare->new( {
                   lists    => [\@Al, \@Bob, \@Carmen, \@Don, \@Ed],
               } );

           or

               $lcm = List::Compare->new( {
                   lists    => [\@Al, \@Bob, \@Carmen, \@Don, \@Ed],
                   unsorted => 1,
               } );

       •   Multiple Mode Methods Analogous to Regular and Accelerated Mode Methods

           Each List::Compare method available in the Regular and Accelerated cases has an
           analogue in the Multiple case.  However, the results produced usually require more
           careful specification.

           Note:  Certain of the following methods available in List::Compare's Multiple mode
           take optional numerical arguments where those numbers represent the index position of
           a particular list in the list of arguments passed to the constructor.  To specify this
           index position correctly,

           •   start the count at 0 (as is customary with Perl array indices); and

           •   do not count any unsorted option ('-u' or '--unsorted') preceding the array
               references in the constructor's own argument list.

           Example:

               $lcmex = List::Compare->new('--unsorted', \@alpha, \@beta, \@gamma);

           For the purpose of supplying a numerical argument to a method which optionally takes
           such an argument, '--unsorted' is skipped, @alpha is 0, @beta is 1, and so forth.

           •   "get_intersection()"

               Get those items found in each of the lists passed to the constructor (their
               intersection):

                   @intersection = $lcm->get_intersection;

           •   "get_union()"

               Get those items found in any of the lists passed to the constructor (their union):

                   @union = $lcm->get_union;

           •   "get_unique()"

               To get those items which appear only in one particular list, provide
               "get_unique()" with that list's index position in the list of arguments passed to
               the constructor (not counting any '-u' or '--unsorted' option).

               Example:  @Carmen has index position 2 in the constructor's @_.  To get elements
               unique to @Carmen:

                   @Lonly = $lcm->get_unique(2);

               If no index position is passed to "get_unique()" it will default to 0 and report
               items unique to the first list passed to the constructor.

           •   "get_complement()"

               To get those items which appear in any list other than one particular list,
               provide "get_complement()" with that list's index position in the list of
               arguments passed to the constructor (not counting any '-u' or '--unsorted'
               option).

               Example:  @Don has index position 3 in the constructor's @_.  To get elements not
               found in @Don:

                   @Ronly = $lcm->get_complement(3);

               If no index position is passed to "get_complement()" it will default to 0 and
               report items found in any list other than the first list passed to the
               constructor.

           •   "get_symmetric_difference()"

               Get those items each of which appears in only one of the lists passed to the
               constructor (their symmetric_difference);

                   @LorRonly = $lcm->get_symmetric_difference;

           •   "get_bag()"

               Make a bag of all items found in any list.  The bag differs from the lists' union
               in that it holds as many copies of individual elements as appear in the original
               lists.

                   @bag = $lcm->get_bag;

           •   Return reference instead of list

               An alternative approach to the above methods:  If you do not immediately require
               an array as the return value of the method call, but simply need a reference to an
               array, use one of the following parallel methods:

                   $intersection_ref = $lcm->get_intersection_ref;
                   $union_ref        = $lcm->get_union_ref;
                   $Lonly_ref        = $lcm->get_unique_ref(2);
                   $Ronly_ref        = $lcm->get_complement_ref(3);
                   $LorRonly_ref     = $lcm->get_symmetric_difference_ref;
                   $bag_ref          = $lcm->get_bag_ref;

           •   "is_LsubsetR()"

               To determine whether one particular list is a subset of another list passed to the
               constructor, provide "is_LsubsetR()" with the index position of the presumed
               subset (ignoring any unsorted option), followed by the index position of the
               presumed superset.

               Example:  To determine whether @Ed is a subset of @Carmen, call:

                   $LR = $lcm->is_LsubsetR(4,2);

               A true value (1) is returned if the left-hand list is a subset of the right-hand
               list; a false value (0) is returned otherwise.

               If no arguments are passed, "is_LsubsetR()" defaults to "(0,1)" and compares the
               first two lists passed to the constructor.

           •   "is_LequivalentR()"

               To determine whether any two particular lists are equivalent to each other,
               provide "is_LequivalentR" with their index positions in the list of arguments
               passed to the constructor (ignoring any unsorted option).

               Example:  To determine whether @Don and @Ed are equivalent, call:

                   $eqv = $lcm->is_LequivalentR(3,4);

               A true value (1) is returned if the lists are equivalent; a false value (0)
               otherwise.

               If no arguments are passed, "is_LequivalentR" defaults to "(0,1)" and compares the
               first two lists passed to the constructor.

           •   "is_LdisjointR()"

               To determine whether any two particular lists are disjoint from each other (i.e.,
               have no members in common), provide "is_LdisjointR" with their index positions in
               the list of arguments passed to the constructor (ignoring any unsorted option).

               Example:  To determine whether @Don and @Ed are disjoint, call:

                   $disj = $lcm->is_LdisjointR(3,4);

               A true value (1) is returned if the lists are equivalent; a false value (0)
               otherwise.

               If no arguments are passed, "is_LdisjointR" defaults to "(0,1)" and compares the
               first two lists passed to the constructor.

           •   "print_subset_chart()"

               Pretty-print a chart showing the subset relationships among the various source
               lists:

                   $lcm->print_subset_chart;

           •   "print_equivalence_chart()"

               Pretty-print a chart showing the equivalence relationships among the various
               source lists:

                   $lcm->print_equivalence_chart;

           •   "is_member_which()"

               Determine in which (if any) of the lists passed to the constructor a given string
               can be found.  In list context, return a list of those indices in the
               constructor's argument list (ignoring any unsorted option) corresponding to i
               lists holding the string being tested.

                   @memb_arr = $lcm->is_member_which('abel');

               In the example above, @memb_arr will be:

                   ( 0 )

               because 'abel' is found only in @Al which holds position 0 in the list of
               arguments passed to "new()".

           •   "is_member_which_ref()"

               As with other List::Compare methods which return a list, you may wish the above
               method returned a (scalar) reference to an array holding the list:

                   $memb_arr_ref = $lcm->is_member_which_ref('jerky');

               In the example above, $memb_arr_ref will be:

                   [ 3, 4 ]

               because 'jerky' is found in @Don and @Ed, which hold positions 3 and 4,
               respectively, in the list of arguments passed to "new()".

               Note:  methods "is_member_which()" and "is_member_which_ref" test only one string
               at a time and hence take only one argument.  To test more than one string at a
               time see the next method, "are_members_which()".

           •   "are_members_which()"

               Determine in "which" (if any) of the lists passed to the constructor one or more
               given strings can be found.  The strings to be tested are placed in an anonymous
               array, a reference to which is passed to the method.

                   $memb_hash_ref =
                       $lcm->are_members_which([ qw| abel baker fargo hilton zebra | ]);

               Note:  In versions of List::Compare prior to 0.25 (April 2004), the strings to be
               tested could be passed as a flat list.  This is no longer possible; the argument
               must now be a reference to an anonymous array.

               The return value is a reference to a hash of arrays.  The key for each element in
               this hash is the string being tested.  Each element's value is a reference to an
               anonymous array whose elements are those indices in the constructor's argument
               list corresponding to lists holding the strings being tested.

               In the two examples above, $memb_hash_ref will be:

                   {
                        abel     => [ 0             ],
                        baker    => [ 0, 1          ],
                        fargo    => [ 0, 1, 2, 3, 4 ],
                        hilton   => [    1, 2       ],
                        zebra    => [               ],
                   };

               Note:  "are_members_which()" can take more than one argument; "is_member_which()"
               and "is_member_which_ref()" each take only one argument.  "are_members_which()"
               returns a hash reference; the other methods return either a list or a reference to
               an array holding that list, depending on context.

           •   "is_member_any()"

               Determine whether a given string can be found in any of the lists passed as
               arguments to the constructor.

                   $found = $lcm->is_member_any('abel');

               Return 1 if a specified string can be found in any of the lists and 0 if not.

               In the example above, $found will be 1 because 'abel' is found in one or more of
               the lists passed as arguments to "new()".

           •   "are_members_any()"

               Determine whether a specified string or strings can be found in any of the lists
               passed as arguments to the constructor.  The strings to be tested are placed in an
               array (anonymous or named), a reference to which is passed to the method.

                   $memb_hash_ref = $lcm->are_members_any([ qw| abel baker fargo hilton zebra | ]);

               Note:  In versions of List::Compare prior to 0.25 (April 2004), the strings to be
               tested could be passed as a flat list.  This is no longer possible; the argument
               must now be a reference to an anonymous array.

               The return value is a reference to a hash where an element's key is the string
               being tested and the element's value is 1 if the string can be found in "any" of
               the lists and 0 if not.  In the two examples above, $memb_hash_ref will be:

                   {
                        abel     => 1,
                        baker    => 1,
                        fargo    => 1,
                        hilton   => 1,
                        zebra    => 0,
                   };

               "zebra"'s value will be 0 because "zebra" is not found in any of the lists passed
               as arguments to "new()".

           •   "get_version()"

               Return current List::Compare version number:

                   $vers = $lcm->get_version;

       •   Multiple Mode Methods Not Analogous to Regular and Accelerated Mode Methods

           •   "get_nonintersection()"

               Get those items found in any of the lists passed to the constructor which do not
               appear in all of the lists (i.e., all items except those found in the intersection
               of the lists):

                   @nonintersection = $lcm->get_nonintersection;

           •   "get_shared()"

               Get those items which appear in more than one of the lists passed to the
               constructor (i.e., all items except those found in their symmetric difference);

                   @shared = $lcm->get_shared;

           •   "get_nonintersection_ref()"

               If you only need a reference to an array as a return value rather than a full
               array, use the following alternative methods:

                   $nonintersection_ref = $lcm->get_nonintersection_ref;
                   $shared_ref = $lcm->get_shared_ref;

           •   "get_unique_all()"

               Get a reference to an array of array references where each of the interior arrays
               holds the list of those items unique to the list passed to the constructor with
               the same index position.

                   $unique_all_ref = $lcm->get_unique_all();

               In the example above, $unique_all_ref will hold:

                   [
                       [ qw| abel | ],
                       [ ],
                       [ qw| jerky | ],
                       [ ],
                       [ ],
                   ]

           •   "get_complement_all()"

               Get a reference to an array of array references where each of the interior arrays
               holds the list of those items in the complement to the list passed to the
               constructor with the same index position.

                   $complement_all_ref = $lcm->get_complement_all();

               In the example above, $complement_all_ref will hold:

                   [
                       [ qw| hilton icon jerky | ],
                       [ qw| abel icon jerky | ],
                       [ qw| abel baker camera delta edward | ],
                       [ qw| abel baker camera delta edward jerky | ],
                       [ qw| abel baker camera delta edward jerky | ],
                   ]

   Multiple Accelerated Case:  Compare Three or More Lists but Request Only a Single Comparison
       among the Lists
       •   Constructor "new()"

           If you are certain that you will only want the results of a single comparison among
           three or more lists, computation may be accelerated by passing '-a' or
           "'--accelerated" as the first argument to the constructor.

               @Al     = qw(abel abel baker camera delta edward fargo golfer);
               @Bob    = qw(baker camera delta delta edward fargo golfer hilton);
               @Carmen = qw(fargo golfer hilton icon icon jerky kappa);
               @Don    = qw(fargo icon jerky);
               @Ed     = qw(fargo icon icon jerky);

               $lcma = List::Compare->new('-a',
                           \@Al, \@Bob, \@Carmen, \@Don, \@Ed);

           As with List::Compare's other cases, should you not need to have a sorted list
           returned by a List::Compare method, you may achieve a speed boost by constructing the
           object with the unsorted option:

               $lcma = List::Compare->new('-u', '-a',
                           \@Al, \@Bob, \@Carmen, \@Don, \@Ed);

           or

               $lcma = List::Compare->new('--unsorted', '--accelerated',
                           \@Al, \@Bob, \@Carmen, \@Don, \@Ed);

           As was the case with List::Compare's Multiple mode, do not count the unsorted option
           ('-u' or '--unsorted') or the accelerated option ('-a' or '--accelerated') when
           determining the index position of a particular list in the list of array references
           passed to the constructor.

           Example:

               $lcmaex = List::Compare->new('--unsorted', '--accelerated',
                              \@alpha, \@beta, \@gamma);

       •   Alternative Constructor

           The 'single hashref' format may be used to construct a List::Compare object which
           calls for accelerated processing of three or more lists at once:

               $lcmaex = List::Compare->new( {
                   accelerated => 1,
                   lists       => [\@alpha, \@beta, \@gamma],
               } );

           or

               $lcmaex = List::Compare->new( {
                   unsorted    => 1,
                   accelerated => 1,
                   lists       => [\@alpha, \@beta, \@gamma],
               } );

       •   Methods

           For the purpose of supplying a numerical argument to a method which optionally takes
           such an argument, '--unsorted' and "'--accelerated" are skipped, @alpha is 0, @beta is
           1, and so forth.  To get a list of those items unique to @gamma, you would call:

               @gamma_only = $lcmaex->get_unique(2);

   Passing Seen-hashes to the Constructor Instead of Arrays
       •   When Seen-Hashes Are Already Available to You

           Suppose that in a particular Perl program, you had to do extensive munging of data
           from an external source and that, once you had correctly parsed a line of data, it was
           easier to assign that datum to a hash than to an array.  More specifically, suppose
           that you used each datum as the key to an element of a lookup table in the form of a
           seen-hash:

              my %Llist = (
                  abel     => 2,
                  baker    => 1,
                  camera   => 1,
                  delta    => 1,
                  edward   => 1,
                  fargo    => 1,
                  golfer   => 1,
              );

              my %Rlist = (
                  baker    => 1,
                  camera   => 1,
                  delta    => 2,
                  edward   => 1,
                  fargo    => 1,
                  golfer   => 1,
                  hilton   => 1,
              );

           In other words, suppose it was more convenient to compute a lookup table implying a
           list than to compute that list explicitly.

           Since in almost all cases List::Compare takes the elements in the arrays passed to its
           constructor and internally assigns them to elements in a seen-hash, why shouldn't you
           be able to pass (references to) seen-hashes directly to the constructor and avoid
           unnecessary array assignments before the constructor is called?

       •   Constructor "new()"

           You can now do so:

               $lcsh = List::Compare->new(\%Llist, \%Rlist);

       •   Methods

           All of List::Compare's output methods are supported without further modification when
           references to seen-hashes are passed to the constructor.

               @intersection         = $lcsh->get_intersection;
               @union                = $lcsh->get_union;
               @Lonly                = $lcsh->get_unique;
               @Ronly                = $lcsh->get_complement;
               @LorRonly             = $lcsh->get_symmetric_difference;
               @bag                  = $lcsh->get_bag;
               $intersection_ref     = $lcsh->get_intersection_ref;
               $union_ref            = $lcsh->get_union_ref;
               $Lonly_ref            = $lcsh->get_unique_ref;
               $Ronly_ref            = $lcsh->get_complement_ref;
               $LorRonly_ref         = $lcsh->get_symmetric_difference_ref;
               $bag_ref              = $lcsh->get_bag_ref;
               $LR                   = $lcsh->is_LsubsetR;
               $RL                   = $lcsh->is_RsubsetL;
               $eqv                  = $lcsh->is_LequivalentR;
               $disj                 = $lcsh->is_LdisjointR;
                                       $lcsh->print_subset_chart;
                                       $lcsh->print_equivalence_chart;
               @memb_arr             = $lsch->is_member_which('abel');
               $memb_arr_ref         = $lsch->is_member_which_ref('baker');
               $memb_hash_ref        = $lsch->are_members_which(
                                           [ qw| abel baker fargo hilton zebra | ]);
               $found                = $lsch->is_member_any('abel');
               $memb_hash_ref        = $lsch->are_members_any(
                                           [ qw| abel baker fargo hilton zebra | ]);
               $vers                 = $lcsh->get_version;
               $unique_all_ref       = $lcsh->get_unique_all();
               $complement_all_ref   = $lcsh->get_complement_all();

       •   Accelerated Mode and Seen-Hashes

           To accelerate processing when you want only a single comparison among two or more
           lists, you can pass '-a' or "'--accelerated" to the constructor before passing
           references to seen-hashes.

               $lcsha = List::Compare->new('-a', \%Llist, \%Rlist);

           To compare three or more lists simultaneously, pass three or more references to seen-
           hashes.  Thus,

               $lcshm = List::Compare->new(\%Alpha, \%Beta, \%Gamma);

           will generate meaningful comparisons of three or more lists simultaneously.

       •   Unsorted Results and Seen-Hashes

           If you do not need sorted lists returned, pass '-u' or "--unsorted" to the constructor
           before passing references to seen-hashes.

               $lcshu  = List::Compare->new('-u', \%Llist, \%Rlist);
               $lcshau = List::Compare->new('-u', '-a', \%Llist, \%Rlist);
               $lcshmu = List::Compare->new('--unsorted', \%Alpha, \%Beta, \%Gamma);

           As was true when we were using List::Compare's Multiple and Multiple Accelerated
           modes, do not count any unsorted or accelerated option when determining the array
           index of a particular seen-hash reference passed to the constructor.

       •   Alternative Constructor

           The 'single hashref' form of constructor is also available to build List::Compare
           objects where seen-hashes are used as arguments:

               $lcshu  = List::Compare->new( {
                   unsorted => 1,
                   lists    => [\%Llist, \%Rlist],
               } );

               $lcshau = List::Compare->new( {
                   unsorted    => 1,
                   accelerated => 1,
                   lists       => [\%Llist, \%Rlist],
               } );

               $lcshmu = List::Compare->new( {
                   unsorted => 1,
                   lists    => [\%Alpha, \%Beta, \%Gamma],
               } );

DISCUSSION: Principles

   General Comments
       List::Compare is an object-oriented implementation of very common Perl code (see "History,
       References and Development" below) used to determine interesting relationships between two
       or more lists at a time.  A List::Compare object is created and automatically computes the
       values needed to supply List::Compare methods with appropriate results.  In the current
       implementation List::Compare methods will return new lists containing the items found in
       any designated list alone (unique), any list other than a designated list (complement),
       the intersection and union of all lists and so forth.  List::Compare also has (a) methods
       to return Boolean values indicating whether one list is a subset of another and whether
       any two lists are equivalent to each other (b) methods to pretty-print very simple charts
       displaying the subset and equivalence relationships among lists.

       Except for List::Compare's "get_bag()" method, multiple instances of an element in a given
       list count only once with respect to computing the intersection, union, etc. of the two
       lists.  In particular, List::Compare considers two lists as equivalent if each element of
       the first list can be found in the second list and vice versa.  'Equivalence' in this
       usage takes no note of the frequency with which elements occur in either list or their
       order within the lists.  List::Compare asks the question:  Did I see this item in this
       list at all?  Only when you use "List::Compare::get_bag()" to compute a bag holding the
       two lists do you ask the question:  How many times did this item occur in this list?

   List::Compare Modes
       In its current implementation List::Compare has four modes of operation.

       •   Regular Mode

           List::Compare's Regular mode is based on List::Compare v0.11 -- the first version of
           List::Compare released to CPAN (June 2002).  It compares only two lists at a time.
           Internally, its initializer does all computations needed to report any desired
           comparison and its constructor stores the results of these computations.  Its public
           methods merely report these results.

           This approach has the advantage that if you need to examine more than one form of
           comparison between two lists (e.g., the union, intersection and symmetric difference
           of two lists), the comparisons are pre-calculated.  This approach is efficient because
           certain types of comparison presuppose that other types have already been calculated.
           For example, to calculate the symmetric difference of two lists, one must first
           determine the items unique to each of the two lists.

       •   Accelerated Mode

           The current implementation of List::Compare offers you the option of getting even
           faster results provided that you only need the result from a single form of comparison
           between two lists. (e.g., only the union -- nothing else).  In the Accelerated mode,
           List::Compare's initializer does no computation and its constructor stores only
           references to the two source lists.  All computation needed to report results is
           deferred to the method calls.

           The user selects this approach by passing the option flag '-a' to the constructor
           before passing references to the two source lists.  List::Compare notes the option
           flag and silently switches into Accelerated mode.  From the perspective of the user,
           there is no further difference in the code or in the results.

           Benchmarking suggests that List::Compare's Accelerated mode (a) is faster than its
           Regular mode when only one comparison is requested; (b) is about as fast as Regular
           mode when two comparisons are requested; and (c) becomes considerably slower than
           Regular mode as each additional comparison above two is requested.

       •   Multiple Mode

           List::Compare now offers the possibility of comparing three or more lists at a time.
           Simply store the extra lists in arrays and pass references to those arrays to the
           constructor.  List::Compare detects that more than two lists have been passed to the
           constructor and silently switches into Multiple mode.

           As described in the Synopsis above, comparing more than two lists at a time offers you
           a wider, more complex palette of comparison methods.  Individual items may appear in
           just one source list, in all the source lists, or in some number of lists between one
           and all.  The meaning of 'union', 'intersection' and 'symmetric difference' is
           conceptually unchanged when you move to multiple lists because these are properties of
           all the lists considered together.  In contrast, the meaning of 'unique',
           'complement', 'subset' and 'equivalent' changes because these are properties of one
           list compared with another or with all the other lists combined.

           List::Compare takes this complexity into account by allowing you to pass arguments to
           the public methods requesting results with respect to a specific list (for
           "get_unique()" and "get_complement()") or a specific pair of lists (for
           "is_LsubsetR()" and "is_LequivalentR()").

           List::Compare further takes this complexity into account by offering the new methods
           "get_shared()" and "get_nonintersection()" described in the Synopsis above.

       •   Multiple Accelerated Mode

           Beginning with version 0.25, introduced in April 2004, List::Compare offers the
           possibility of accelerated computation of a single comparison among three or more
           lists at a time.  Simply store the extra lists in arrays and pass references to those
           arrays to the constructor preceded by the '-a' argument as was done with the simple
           (two lists only) accelerated mode.  List::Compare detects that more than two lists
           have been passed to the constructor and silently switches into Multiple Accelerated
           mode.

       •   Unsorted Option

           When List::Compare is used to return lists representing various comparisons of two or
           more lists (e.g., the lists' union or intersection), the lists returned are, by
           default, sorted using Perl's default "sort" mode: ASCII-betical sorting.  Sorting
           produces results which are more easily human-readable but may entail a performance
           cost.

           Should you not need sorted results, you can avoid the potential performance cost by
           calling List::Compare's constructor using the unsorted option.  This is done by
           calling '-u' or '--unsorted' as the first argument passed to the constructor, i.e., as
           an argument called before any references to lists are passed to the constructor.

           Note that if are calling List::Compare in the Accelerated or Multiple Accelerated mode
           and wish to have the lists returned in unsorted order, you first pass the argument for
           the unsorted option ('-u' or '--unsorted') and then pass the argument for the
           Accelerated mode ('-a' or '--accelerated').

   Miscellaneous Methods
       It would not really be appropriate to call "get_shared()" and "get_nonintersection()" in
       Regular or Accelerated mode since they are conceptually based on the notion of comparing
       more than two lists at a time.  However, there is always the possibility that a user may
       be comparing only two lists (accelerated or not) and may accidentally call one of those
       two methods.  To prevent fatal run-time errors and to caution you to use a more
       appropriate method, these two methods are defined for Regular and Accelerated modes so as
       to return suitable results but also generate a carp message that advise you to re-code.

       Similarly, the method "is_RsubsetL()" is appropriate for the Regular and Accelerated modes
       but is not really appropriate for Multiple mode.  As a defensive maneuver, it has been
       defined for Multiple mode so as to return suitable results but also to generate a carp
       message that advises you to re-code.

       In List::Compare v0.11 and earlier, the author provided aliases for various methods based
       on the supposition that the source lists would be referred to as 'A' and 'B'.  Now that
       you can compare more than two lists at a time, the author feels that it would be more
       appropriate to refer to the elements of two-argument lists as the left-hand and right-hand
       elements.  Hence, we are discouraging the use of methods such as "get_Aonly()",
       "get_Bonly()" and "get_AorBonly()" as aliases for "get_unique()", "get_complement()" and
       "get_symmetric_difference()".  However, to guarantee backwards compatibility for the vast
       audience of Perl programmers using earlier versions of List::Compare (all 10e1 of you)
       these and similar methods for subset relationships are still defined.

   List::Compare::SeenHash Discontinued Beginning with Version 0.26
       Prior to v0.26, introduced April 11, 2004, if a user wished to pass references to seen-
       hashes to List::Compare's constructor rather than references to arrays, he or she had to
       call a different, parallel module: List::Compare::SeenHash.  The code for that looked like
       this:

           use List::Compare::SeenHash;

           my %Llist = (
              abel     => 2,
              baker    => 1,
              camera   => 1,
              delta    => 1,
              edward   => 1,
              fargo    => 1,
              golfer   => 1,
           );

           my %Rlist = (
              baker    => 1,
              camera   => 1,
              delta    => 2,
              edward   => 1,
              fargo    => 1,
              golfer   => 1,
              hilton   => 1,
           );

           my $lcsh = List::Compare::SeenHash->new(\%Llist, \%Rlist);

       List::Compare::SeenHash is deprecated beginning with version 0.26.  All its functionality
       (and more) has been implemented in List::Compare itself, since a user can now pass either
       a series of array references or a series of seen-hash references to List::Compare's
       constructor.

       To simplify future maintenance of List::Compare, List::Compare::SeenHash.pm will no longer
       be distributed with List::Compare, nor will the files in the test suite which tested
       List::Compare::SeenHash upon installation be distributed.

       Should you still need List::Compare::SeenHash, use version 0.25 from CPAN, or simply edit
       your Perl programs which used List::Compare::SeenHash.  Those scripts may be edited
       quickly with, for example, this editing command in Unix text editor vi:

           :1,$s/List::Compare::SeenHash/List::Compare/gc

   A Non-Object-Oriented Interface:  List::Compare::Functional
       Version 0.21 of List::Compare introduced List::Compare::Functional, a functional (i.e.,
       non-object-oriented) interface to list comparison functions.  List::Compare::Functional
       supports the same functions currently supported by List::Compare.  It works similar to
       List::Compare's Accelerated and Multiple Accelerated modes (described above), bit it does
       not require use of the '-a' flag in the function call.  List::Compare::Functional will
       return unsorted comparisons of two lists by passing '-u' or '--unsorted' as the first
       argument to the function.  Please see the documentation for List::Compare::Functional to
       learn how to import its functions into your main package.

ASSUMPTIONS AND QUALIFICATIONS

       The program was created with Perl 5.6. The use of h2xs to prepare the module's template
       installed "require 5.005_62;" at the top of the module.  This has been commented out in
       the actual module as the code appears to be compatible with earlier versions of Perl; how
       earlier the author cannot say.  In particular, the author would like the module to be
       installable on older versions of MacPerl.  As is, the author has successfully installed
       the module on Linux, Windows 9x and Windows 2000.  See
       <http://testers.cpan.org/show/List-Compare.html> for a list of other systems on which this
       version of List::Compare has been tested and installed.

HISTORY, REFERENCES AND DEVELOPMENT

   The Code Itself
       List::Compare is based on code presented by Tom Christiansen & Nathan Torkington in Perl
       Cookbook <http://www.oreilly.com/catalog/cookbook/> (a.k.a. the 'Ram' book), O'Reilly &
       Associates, 1998, Recipes 4.7 and 4.8.  Similar code is presented in the Camel book:
       Programming Perl, by Larry Wall, Tom Christiansen, Jon Orwant.
       <http://www.oreilly.com/catalog/pperl3/>, 3rd ed, O'Reilly & Associates, 2000.  The list
       comparison code is so basic and Perlish that I suspect it may have been written by Larry
       himself at the dawn of Perl time.  The "get_bag()" method was inspired by Jarkko
       Hietaniemi's Set::Bag module and Daniel Berger's Set::Array module, both available on
       CPAN.

       List::Compare's original objective was simply to put this code in a modular, object-
       oriented framework.  That framework, not surprisingly, is taken mostly from Damian
       Conway's Object Oriented Perl <http://www.manning.com/Conway/index.html>, Manning
       Publications, 2000.

       With the addition of the Accelerated, Multiple and Multiple Accelerated modes,
       List::Compare expands considerably in both size and capabilities.  Nonetheless,  Tom and
       Nat's Cookbook code still lies at its core: the use of hashes as look-up tables to record
       elements seen in lists.  Please note:  List::Compare is not concerned with any concept of
       'equality' among lists which hinges upon the frequency with which, or the order in which,
       elements appear in the lists to be compared.  If this does not meet your needs, you should
       look elsewhere or write your own module.

   The Inspiration
       I realized the usefulness of putting the list comparison code into a module while
       preparing an introductory level Perl course given at the New School University's Computer
       Instruction Center in April-May 2002.  I was comparing lists left and right.  When I found
       myself writing very similar functions in different scripts, I knew a module was lurking
       somewhere.  I learned the truth of the mantra ''Repeated Code is a Mistake'' from a 2001
       talk by Mark-Jason Dominus <http://perl.plover.com/> to the New York Perlmongers
       <http://ny.pm.org/>.  See <http://www.perl.com/pub/a/2000/11/repair3.html>.

       The first public presentation of this module took place at Perl Seminar New York
       <http://groups.yahoo.com/group/perlsemny> on May 21, 2002.  Comments and suggestions were
       provided there and since by Glenn Maciag, Gary Benson, Josh Rabinowitz, Terrence Brannon
       and Dave Cross.

       The placement in the installation tree of Test::ListCompareSpecial came as a result of a
       question answered by Michael Graham in his talk ''Test::More to Test::Extreme'' given at
       Yet Another Perl Conference::Canada in Ottawa, Ontario, on May 16, 2003.

       In May-June 2003, Glenn Maciag made valuable suggestions which led to changes in method
       names and documentation in v0.20.

       Another presentation at Perl Seminar New York in October 2003 prompted me to begin
       planning List::Compare::Functional.

       In a November 2003 Perl Seminar New York presentation, Ben Holtzman discussed the
       performance costs entailed in Perl's "sort" function.  This led me to ask, ''Why should a
       user of List::Compare pay this performance cost if he or she doesn't need a human-readable
       list as a result (as would be the case if the list returned were used as the input into
       some other function)?''  This led to the development of List::Compare's unsorted option.

       An April 2004 offer by Kevin Carlson to write an article for The Perl Journal
       (<http://tpj.com>) led me to re-think whether a separate module (the former
       List::Compare::SeenHash) was truly needed when a user wanted to provide the constructor
       with references to seen-hashes rather than references to arrays.  Since I had already
       adapted List::Compare::Functional to accept both kinds of arguments, I adapted
       List::Compare in the same manner.  This meant that List::Compare::SeenHash and its related
       installation tests could be deprecated and deleted from the CPAN distribution.

       A remark by David H. Adler at a New York Perlmongers meeting in April 2004 led me to
       develop the 'single hashref' alternative constructor format, introduced in version 0.29
       the following month.

       Presentations at two different editions of Yet Another Perl Conference (YAPC) inspired the
       development of List::Compare versions 0.30 and 0.31.  I was selected to give a talk on
       List::Compare at YAPC::NA::2004 in Buffalo.  This spurred me to improve certain aspects of
       the documentation.  Version 0.31 owes its inspiration to one talk at the Buffalo YAPC and
       one earlier talk at YAPC::EU::2003 in Paris.  In Paris I heard Paul Johnson speak on his
       CPAN module Devel::Cover and on coverage analysis more generally.  That material was over
       my head at that time, but in Buffalo I heard Andy Lester discuss Devel::Cover as part of
       his discussion of testing and of the Phalanx project (<http://qa.perl.org/phalanx>).  This
       time I got it, and when I returned from Buffalo I applied Devel::Cover to List::Compare
       and wrote additional tests to improve its subroutine and statement coverage.  In addition,
       I added two new methods, "get_unique_all" and "get_complement_all".  In writing these two
       methods, I followed a model of test-driven development much more so than in earlier
       versions of List::Compare and my other CPAN modules.  The result?  List::Compare's test
       suite grew by over 3300 tests to nearly 23,000 tests.

       At the Second New York Perl Hackathon (May 02 2015), a project was created to request
       performance improvements in certain List::Compare functions
       (<https://github.com/nyperlmongers/nyperlhackathon2015/wiki/List-Compare-Performance-Improvements>).
       Hackathon participant Michael Rawson submitted a pull request with changes to
       List::Compare::Base::_Auxiliary.  After these revisions were benchmarked, a patch
       embodying the pull request was accepted, leading to CPAN version 0.53.

   If You Like List::Compare, You'll Love ...
       While preparing this module for distribution via CPAN, I had occasion to study a number of
       other modules already available on CPAN.  Each of these modules is more sophisticated than
       List::Compare -- which is not surprising since all that List::Compare originally aspired
       to do was to avoid typing Cookbook code repeatedly.  Here is a brief description of the
       features of these modules.  (Warning:  The following discussion is only valid as of June
       2002.  Some of these modules may have changed since then.)

       •   Algorithm::Diff - Compute 'intelligent' differences between two files/lists
           (<http://search.cpan.org/dist/Algorithm-Diff/>)

           Algorithm::Diff is a sophisticated module originally written by Mark-Jason Dominus,
           later maintained by Ned Konz, now maintained by Tye McQueen. Think of the Unix "diff"
           utility  and you're on the right track.  Algorithm::Diff exports methods such as
           "diff", which ''computes the smallest set of additions and deletions necessary to turn
           the first sequence into the second, and returns a description of these changes.''
           Algorithm::Diff is mainly concerned with the sequence of elements within two lists.
           It does not export functions for intersection, union, subset status, etc.

       •   Array::Compare - Perl extension for comparing arrays
           (<http://search.cpan.org/dist/Array-Compare/>)

           Array::Compare, by Dave Cross, asks whether two arrays are the same or different by
           doing a "join" on each string with a separator character and comparing the resulting
           strings.  Like List::Compare, it is an object-oriented module.  A sophisticated
           feature of Array::Compare is that it allows you to specify how 'whitespace' in an
           array (an element which is undefined, the empty string, or whitespace within an
           element) should be evaluated for purpose of determining equality or difference.    It
           does not directly provide methods for intersection and union.

       •   Data::Compare - compare perl data structures
           (<http://search.cpan.org/dist/Data-Compare/>)

           This library compares Perl data structures recursively.  Comes recommended by Slaven
           Rezić!

       •   List::Util - A selection of general-utility list subroutines
           (<http://search.cpan.org/dist/Scalar-List-Utils/>)

           List::Util, by Graham Barr, exports a variety of simple, useful functions for
           operating on one list at a time.    The "min" function returns the lowest numerical
           value in a list; the "max" function returns the highest value; and so forth.
           List::Compare differs from List::Util in that it is object-oriented and that it works
           on two strings at a time rather than just one -- but it aims to be as simple and
           useful as List::Util.  List::Util will be included in the standard Perl distribution
           as of Perl 5.8.0.

           Lists::Util (<http://search.cpan.org/dist/List-MoreUtils/>), by Tassilo von Parseval,
           building on code by Terrence Brannon, provides methods which extend List::Util's
           functionality.

       •   Quantum::Superpositions (<http://search.cpan.org/dist/Quantum-Superpositions/>),
           originally by Damian Conway, now maintained by Steven Lembark is useful if, in
           addition to comparing lists, you need to emulate quantum supercomputing as well.  Not
           for the eigen-challenged.

       •   Set::Scalar - basic set operations (<http://search.cpan.org/dist/Set-Scalar/>)

           Set::Bag - bag (multiset) class (<http://search.cpan.org/dist/Set-Bag/>)

           Both of these modules are by Jarkko Hietaniemi.  Set::Scalar has methods to return the
           intersection, union, difference and symmetric difference of two sets, as well as
           methods to return items unique to a first set and complementary to it in a second set.
           It has methods for reporting considerably more variants on subset status than does
           List::Compare.  However, benchmarking suggests that List::Compare, at least in Regular
           mode, is considerably faster than Set::Scalar for those comparison methods which
           List::Compare makes available.

           Set::Bag enables one to deal more flexibly with the situation in which one has more
           than one instance of an element in a list.

       •   Set::Array - Arrays as objects with lots of handy methods (including set comparisons)
           and support for method chaining.  (<http://search.cpan.org/dist/Set-Array/>)

           Set::Array, by Daniel Berger, now maintained by Ron Savage, ''aims to provide built-in
           methods for operations that people are always asking how to do,and which already exist
           in languages like Ruby.''  Among the many methods in this module are some for
           intersection, union, etc.  To install Set::Array, you must first install the Want
           module, also available on CPAN.

ADDITIONAL CONTRIBUTORS

       •   Syohei YOSHIDA

           Pull request accepted May 22 2015.

       •   Paulo Custodio

           Pull request accepted June 07 2015, correcting errors in "_subset_subengine()".

BUGS

       There are no bug reports outstanding on List::Compare as of the most recent CPAN upload
       date of this distribution.

SUPPORT

       Please report any bugs by mail to "bug-List-Compare@rt.cpan.org" or through the web
       interface at <http://rt.cpan.org>.

AUTHOR

       James E. Keenan (jkeenan@cpan.org).  When sending correspondence, please include
       'List::Compare' or 'List-Compare' in your subject line.

       Creation date:  May 20, 2002.  Last modification date:  August 16 2020.

       Development repository: <https://github.com/jkeenan/list-compare>

COPYRIGHT

       Copyright (c) 2002-20 James E. Keenan.  United States.  All rights reserved.  This is free
       software and may be distributed under the same terms as Perl itself.

DISCLAIMER OF WARRANTY

       BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE,
       TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE
       COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE ''AS IS'' WITHOUT WARRANTY OF
       ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
       WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO
       THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE
       DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

       IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT
       HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY
       THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,
       INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE
       SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR
       LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY
       OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
       SUCH DAMAGES.