| Current File : //proc/self/root/usr/share/perl5/Algorithm/Merge.pm |
package Algorithm::Merge;
use Algorithm::Diff ();
use Carp;
use strict;
use Data::Dumper;
use vars qw(@EXPORT_OK @ISA $VERSION $REVISION);
$VERSION = '0.08';
$REVISION = (qw$Revision: 1.11 $)[-1];
@EXPORT_OK = qw(diff3 merge traverse_sequences3);
@ISA = qw(Exporter);
sub diag {
main::diag(@_) if($Algorithm::Merge::DEBUG);
}
sub diff3 {
my $pivot = shift; # array ref
my $doca = shift; # array ref
my $docb = shift; # array ref
my $keyGen = shift;
my @ret;
if(@$doca == 0 && @$docb == 0 && @$pivot == 0) {
return [ [ ] ];
}
my $no_change;
# if($keyGen) {
# $no_change = sub {
# if($keyGen->($pivot -> [$_[0]]) ne $keyGen->($doca -> [$_[1]])
# || $keyGen->($pivot -> [$_[0]]) ne $keyGen->($docb -> [$_[2]])
# || $keyGen->($doca -> [$_[1]]) ne $keyGen->($docb -> [$_[2]]))
# {
# croak "No change detected, but elements differ between sequences. Please submit a bug report to jsmith\@cpan.org with a description of the set of sequences which lead to this error.\n";
# }
# push @ret, [ 'u', $pivot -> [$_[0]], $doca -> [$_[1]], $docb -> [$_[2]] ];
# };
# }
# else {
$no_change = sub {
# if($pivot -> [$_[0]] ne $doca -> [$_[1]]
# || $pivot -> [$_[0]] ne $docb -> [$_[2]]
# || $doca -> [$_[1]] ne $docb -> [$_[2]])
# {
# croak "No change detected, but elements differ between sequences. Please submit a bug report to jsmith\@cpan.org with a description of the set of sequences which lead to this error.\n";
# }
push @ret, [ 'u', $pivot -> [$_[0]], $doca -> [$_[1]], $docb -> [$_[2]] ];
};
# }
my $conflict = sub {
my($a, $b, $c);
$a = $pivot -> [$_[0]] if defined $_[0];
$b = $doca -> [$_[1]] if defined $_[1];
$c = $docb -> [$_[2]] if defined $_[2];
push @ret, [ 'c', $a, $b, $c ];
};
my $diff_a = sub {
if(@_ == 1) {
push @ret, [ 'o', $pivot -> [$_[0]], undef, undef ];
}
elsif(@_ == 2) {
push @ret, [ 'o', undef, $doca -> [$_[0]], $docb -> [$_[1]] ];
}
elsif(@_ == 3) {
push @ret, [ 'o', $pivot -> [$_[0]], $doca -> [$_[1]], $docb -> [$_[2]] ];
}
};
my $diff_b = sub {
if(@_ == 1) {
push @ret, [ 'l', undef, $doca -> [$_[0]], undef ];
}
elsif(@_ == 2) {
push @ret, [ 'l', $pivot -> [$_[0]], undef, $docb -> [$_[1]] ];
}
elsif(@_ == 3) {
push @ret, [ 'l', $pivot -> [$_[0]], $doca -> [$_[1]], $docb -> [$_[2]] ];
}
};
my $diff_c = sub {
if(@_ == 1) {
push @ret, [ 'r', undef, undef, (defined($_[0]) ? $docb -> [$_[0]] : undef) ];
}
elsif(@_ == 2) {
push @ret, [ 'r', (defined($_[0]) ? $pivot -> [$_[0]] : undef), (defined($_[1]) ? $doca -> [$_[1]] : undef), undef ];
}
elsif(@_ == 3) {
push @ret, [ 'r', (defined($_[0]) ? $pivot -> [$_[0]] : undef), (defined($_[1]) ? $doca -> [$_[1]] : undef), (defined($_[0]) ? $docb -> [$_[2]] : undef)];
}
};
traverse_sequences3(
$pivot, $doca, $docb,
{
NO_CHANGE => $no_change,
A_DIFF => $diff_a,
B_DIFF => $diff_b,
C_DIFF => $diff_c,
CONFLICT => $conflict,
},
$keyGen, @_
);
if(wantarray) {
return @ret;
}
else {
return \@ret;
}
}
use constant A => 4;
use constant B => 2;
use constant C => 1;
use constant D => 8; # should be an undef
use constant AB_A => 32;
use constant AB_B => 16;
use constant AC_A => 8;
use constant AC_C => 4;
use constant BC_B => 2;
use constant BC_C => 1;
use constant CB_C => 3; # not used in calculations
use constant CB_B => 5; # not used in calculations
my @abc_s;
$abc_s[(A|B)*8+A] = AB_A;
$abc_s[(A|B)*8+B] = AB_B;
$abc_s[(A|C)*8+A] = AC_A;
$abc_s[(A|C)*8+C] = AC_C;
$abc_s[(B|C)*8+B] = BC_B;
$abc_s[(B|C)*8+C] = BC_C;
sub traverse_sequences3 {
my $adoc = shift; # array ref
my $bdoc = shift; # array ref
my $cdoc = shift; # array ref
my $callbacks = shift || {};
my $keyGen = shift;
my $a_diff = $callbacks->{'A_DIFF'} || sub { };
my $b_diff = $callbacks->{'B_DIFF'} || sub { };
my $c_diff = $callbacks->{'C_DIFF'} || sub { };
my $no_change = $callbacks->{'NO_CHANGE'} || sub { };
my $conflict = $callbacks->{'CONFLICT'} || sub { };
my $b_len = scalar(@{$bdoc});
my $c_len = scalar(@{$cdoc});
my $target_len = $b_len < $c_len ? $b_len : $c_len;
my $bc_different_lengths = $b_len != $c_len;
my(@bdoc_save, @cdoc_save);
# make these into traverse_sequences calls
my($left, $right);
my %diffs;
my $ts_callbacks = {
DISCARD_A => sub { # discard left
push @{$diffs{$left}}, $_[0];
},
DISCARD_B => sub { # discard right
push @{$diffs{$right}}, $_[1];
},
};
@diffs{(AB_A, AB_B)} = ([], []);
$left = AB_A; $right = AB_B;
Algorithm::Diff::traverse_sequences( $adoc, $bdoc, $ts_callbacks, $keyGen, @_);
@diffs{(AC_A, AC_C)} = ([], []);
$left = AC_A; $right = AC_C;
Algorithm::Diff::traverse_sequences( $adoc, $cdoc, $ts_callbacks, $keyGen, @_);
if($bc_different_lengths) {
@diffs{(CB_C, CB_B)} = ([], []);
$left = CB_C; $right = CB_B;
Algorithm::Diff::traverse_sequences( $cdoc, $bdoc, $ts_callbacks, $keyGen, @_);
@diffs{(BC_B, BC_C)} = ([], []);
$left = BC_B; $right = BC_C;
Algorithm::Diff::traverse_sequences( $bdoc, $cdoc, $ts_callbacks, $keyGen, @_);
if(join(",", @{$diffs{&CB_B}}) ne join(",", @{$diffs{&BC_B}}) ||
join(",", @{$diffs{&CB_C}}) ne join(",", @{$diffs{&BC_C}}))
{
@bdoc_save = splice @{$bdoc}, $target_len;
@cdoc_save = splice @{$cdoc}, $target_len;
carp "Algorithm::Diff::diff is not symmetric for second and third sequences - results might not be correct";
}
@diffs{(BC_B, BC_C)} = ([], []);
$left = BC_B; $right = BC_C;
Algorithm::Diff::traverse_sequences( $bdoc, $cdoc, $ts_callbacks, $keyGen, @_);
if(scalar(@bdoc_save) || scalar(@cdoc_save)) {
push @{$diffs{&BC_B}}, ($target_len .. $b_len) if $target_len < $b_len;
push @{$diffs{&BC_C}}, ($target_len .. $c_len) if $target_len < $c_len;
push @{$bdoc}, @bdoc_save; undef @bdoc_save;
push @{$cdoc}, @cdoc_save; undef @cdoc_save;
}
}
else {
@diffs{(BC_B, BC_C)} = ([], []);
$left = BC_B; $right = BC_C;
Algorithm::Diff::traverse_sequences( $bdoc, $cdoc, $ts_callbacks, $keyGen, @_);
}
my @pos;
@pos[A, B, C] = (0, 0, 0);
my @sizes;
@sizes[A, B, C] = ( scalar(@{$adoc}), scalar(@{$bdoc}), scalar(@{$cdoc}) );
my @matches;
$#matches = 32;
my $callback = 0;
my $noop = sub { };
# Callback_Map is indexed by the sum of AB_A, AB_B, ..., as indicated by @matches
# this isn't the most efficient, but it's a bit easier to maintain and
# read than if it were broken up into separate arrays
# half the entries are not $noop - it would seem then that no
# entries should be $noop. I need patterns to figure out what the
# other entries are.
my @Callback_Map = (
[ $no_change, A, B, C ], # 0 - no matches
#[ $noop, ], # 1 - BC_C
[ $b_diff, A, C ], # 1 - BC_C
[ $b_diff, B ], #*2 - BC_B
[ $noop, ], # 3 - BC_B BC_C
[ $noop, ], # 4 - AC_C
[ $c_diff, C ], # 5 - AC_C BC_C
[ $noop, ], # 6 - AC_C BC_B
[ $noop, ], # 7 - AC_C BC_B BC_C
[ $a_diff, A ], # 8 - AC_A
[ $noop, ], # 9 - AC_A BC_C
[ $c_diff, A, B ], # 10 - AC_A BC_B
[ $c_diff, A, B, ], # 11 - AC_A BC_B BC_C
[ $noop, ], # 12 - AC_A AC_C
[ $noop, ], # 13 - AC_A AC_C BC_C
[ $c_diff, A, B, ], # 14 - AC_A AC_C BC_B
[ $c_diff, A, B, C ], # 15 - AC_A AC_C BC_B BC_C
[ $noop, ], # 16 - AB_B
[ $no_change, ], # 17 - AB_B BC_C
[ $b_diff, B ], # 18 - AB_B BC_B
[ $noop, ], # 19 - AB_B BC_B BC_C
[ $a_diff, B, C ], # 20 - AB_B AC_C
[ $noop, ], # 21 - AB_B AC_C BC_C
[ $noop, ], # 22 - AB_B AC_C BC_B
[ $conflict, D, B, C ], # 23 - AB_B AC_C BC_B BC_C
[ $b_diff, B ], # 24 - AB_B AC_A
[ $noop, ], # 25 - AB_B AC_A BC_C
[ $c_diff, D, B, C ], # 26 - AB_B AC_A BC_B
[ $noop, ], # 27 - AB_B AC_A BC_B BC_C
[ $a_diff, B, C ], # 28 - AB_B AC_A AC_C
[ $noop, ], # 29 - AB_B AC_A AC_C BC_C
[ $noop, ], # 30 - AB_B AC_A AC_C BC_B
[ $b_diff, B ], # 31 - AB_B AC_A AC_C BC_B BC_C
[ $no_change, A, B, C ], # 32 - AB_A
[ $b_diff, A, C ], # 33 - AB_A BC_C
[ $noop, ], # 34 - AB_A BC_B
[ $b_diff, A, C ], # 35 - AB_A BC_B BC_C
[ $noop, ], # 36 - AB_A AC_C
[ $noop, ], # 37 - AB_A AC_C BC_C
[ $noop, ], # 38 - AB_A AC_C BC_B
[ $noop, ], # 39 - AB_A AC_C BC_B BC_C
[ $a_diff, A, ], # 40 - AB_A AC_A
[ $noop, ], # 41 - AB_A AC_A BC_C
[ $a_diff, A ], # 42 - AB_A AC_A BC_B
[ $noop, ], # 43 - AB_A AC_A BC_B BC_C
[ $noop, ], # 44 - AB_A AC_A AC_C
[ $c_diff, A, D, C ], # 45 - AB_A AC_A AC_C BC_C
[ $noop, ], # 46 - AB_A AC_A AC_C BC_B
[ $noop, ], # 47 - AB_A AC_A AC_C BC_B BC_C
[ $noop, ], # 48 - AB_A AB_B
[ $b_diff, A, C ], # 49 - AB_A AB_B BC_C
[ $noop, ], # 50 - AB_A AB_B BC_B
[ $b_diff, A, B, C ], # 51 - AB_A AB_B BC_B BC_C
[ $a_diff, B, C ], # 52 - AB_A AB_B AC_C
[ $noop, ], # 53 - AB_A AB_B AC_C BC_C
[ $noop, ], # 54 - AB_A AB_B AC_C BC_B
[ $c_diff, C ], # 55 - AB_A AB_B AC_C BC_B BC_C
[ $b_diff, A, C ], # 56 - AB_A AB_B AC_A
[ $noop, ], # 57 - AB_A AB_B AC_A BC_C
[ $b_diff, A, B, D ], # 58 - AB_A AB_B AC_A BC_B
[ $noop, ], # 59 - AB_A AB_B AC_A BC_B BC_C
[ $a_diff, A, B, C ], # 60 - AB_A AB_B AC_A AC_C
[ $conflict, A, D, C ], # 61 - AB_A AB_B AC_A AC_C BC_C
[ $conflict, A, B, D ], # 62 - AB_A AB_B AC_A AC_C BC_B
[ $conflict, A, B, C ], # 63 - AB_A AB_B AC_A AC_C BC_B BC_C
);
my $t; # temporary values
# while we have something to work with...
while((grep { scalar(@{$_}) > 0 } values %diffs)
&& (grep { $pos[$_] < $sizes[$_] } (A, B, C)))
{
@matches[AB_A, AB_B, AC_A, AC_C, BC_B, BC_C] = undef;
foreach my $i (A, B, C) {
foreach my $j (A, B, C) {
next if $i == $j;
$t = $abc_s[($i|$j) * 8 | $i];
$matches[$t] = 1 if @{$diffs{$t}} && $pos[$i] == $diffs{$t} -> [0];
}
}
$callback = 0;
$callback |= $_ foreach grep { $matches[$_] } ( AB_A, AB_B, AC_A, AC_C, BC_B, BC_C );
my @args = @{$Callback_Map[$callback]};
diag(">>>>>> We hit a noop") if @args == 1;
my $f = shift @args;
diag(join "", "callback: $callback - \@pos: ", join(", ", @pos[A, B, C]), "\n");
diag(">>>>>> Callback is a no-op") unless @args;
diag(join "", " matches: ", join(", ", map { defined($_) ? $_ : 'undef' } @matches[AB_A, AB_B, AC_A, AC_C, BC_B, BC_C]), "\n");
diag(join "", " diffs: ", join(", ", map { defined($_) ? $_ : 'undef' } map { $diffs{$_}->[0] } (AB_A, AB_B, AC_A, AC_C, BC_B, BC_C)), "\n");
diag(join "", "args: ", join(", ", map { (qw(- C B - A - - - D))[$_] } @args), "(", join(", ", map { defined($_) ? $_ : 'undef' } @pos[@args]), ")\n");
diag('--------------------');
&{$f}(@pos[@args]);
foreach (@args) {
$pos[$_]++ unless $_ == D;
if($_ eq A) {
shift @{$diffs{&AB_A}} while @{$diffs{&AB_A}} && $diffs{&AB_A}[0] < $pos[$_];# if $matches[AB_A];
shift @{$diffs{&AC_A}} while @{$diffs{&AC_A}} && $diffs{&AC_A}[0] < $pos[$_];#if $matches[AC_A];
} elsif($_ eq B) {
shift @{$diffs{&AB_B}} while @{$diffs{&AB_B}} && $diffs{&AB_B}[0] < $pos[$_];#if $matches[AB_B];
shift @{$diffs{&BC_B}} while @{$diffs{&BC_B}} && $diffs{&BC_B}[0] < $pos[$_];#if $matches[BC_B];
} elsif($_ eq C) {
shift @{$diffs{&AC_C}} while @{$diffs{&AC_C}} && $diffs{&AC_C}[0] < $pos[$_];#if $matches[AC_C];
shift @{$diffs{&BC_C}} while @{$diffs{&BC_C}} && $diffs{&BC_C}[0] < $pos[$_];#if $matches[BC_C];
}
}
last unless @args;
}
my $switch;
my @args;
while(grep { $pos[$_] < $sizes[$_] } (A, B, C)) {
$switch = 0;
@args = ();
foreach my $i (A, B, C) {
if($pos[$i] < $sizes[$i]) {
#warn "$i: $pos[$i] < $sizes[$i]\n";
$switch |= $i;
#warn "switch: $switch\n";
push @args, $pos[$i]++;
}
}
my $match = $switch;
$switch = ( 0, 5, 24, 17, 34, 8, 10, 0 )[$switch];
#main::diag(join"", "callback: $switch - \@pos: ", join(", ", @pos[A, B, C]));
#main::diag(join"", " match: $match");
&{$Callback_Map[$switch][0]}(@args)
if $Callback_Map[$switch];
}
}
sub merge {
my $pivot = shift; # array ref
my $doca = shift; # array ref
my $docb = shift; # array ref
my $callbacks = shift || {};
my $keyGen = shift;
my $conflictCallback = $callbacks -> {'CONFLICT'} || sub ($$) { (
q{<!-- ------ START CONFLICT ------ -->},
(@{$_[0]}),
q{<!-- ---------------------------- -->},
(@{$_[1]}),
q{<!-- ------ END CONFLICT ------ -->},
) };
my $diff = diff3($pivot, $doca, $docb, $keyGen, @_);
# print Data::Dumper -> Dump([$diff]), "\n";
my @ret;
my @conflict = ( [], [] );
foreach my $h (@{$diff}) {
my $i = 0;
#print "op: ", $h -> [0];
if($h -> [0] eq 'c') { # conflict
push @{$conflict[0]}, $h -> [2] if defined $h -> [2];
push @{$conflict[1]}, $h -> [3] if defined $h -> [3];
}
else {
if(@{$conflict[0]} || @{$conflict[1]}) {
push @ret, &$conflictCallback(@conflict);
@conflict = ( [], [] );
}
if($h -> [0] eq 'u') { # unchanged
push @ret, $h -> [2] || $h -> [3];
}
elsif($h -> [0] eq 'o') { # added
push @ret, $h -> [2] if defined $h -> [2];
}
elsif($h -> [0] eq 'l') { # added by left
push @ret, $h -> [2] if defined $h -> [2];
}
elsif($h -> [0] eq 'r') { # added by right
push @ret, $h -> [3] if defined $h -> [3];
}
}
#print " : ", join(" ", @ret), " [$$h[1],$$h[2],$$h[3]]\n";
}
if(@{$conflict[0]} || @{$conflict[1]}) {
push @ret, &$conflictCallback(@conflict);
}
if(wantarray) {
return @ret;
}
return \@ret;
}
__END__
#
# For testing:
#
sub main::diag {
warn join("", @_) , "\n";
}
print join(" ", merge(
#print Data::Dumper -> Dump([
# merge(
# #[qw(a b c d h i j)], # ancestor
# #[qw(a b c d f h i j)], # left
# #[qw(a b c e g )], # right
[qw(0 1 2 3 4 7 9 b)],
[qw(0 6 8 a b)],
[qw(0 1 2 3 5 8 a b)],
##
{
CONFLICT => sub ($$) { (
q{<}, @{$_[0]}, q{|}, @{$_[1]}, q{>}
) },
},
)), "\n";
#)]), "\n";
#print join(" ", @{
# [qw(0 1 @ < 3 | # > 6)]
# }), "\n";
1;
__END__
1;
__END__
=head1 NAME
Algorithm::Merge - Three-way merge and diff
=head1 SYNOPSIS
use Algorithm::Merge qw(merge diff3 traverse_sequences3);
@merged = merge(\@ancestor, \@a, \@b, {
CONFLICT => sub { }
});
@merged = merge(\@ancestor, \@a, \@b, {
CONFLICT => sub { }
}, $key_generation_function);
$merged = merge(\@ancestor, \@a, \@b, {
CONFLICT => sub { }
});
$merged = merge(\@ancestor, \@a, \@b, {
CONFLICT => sub { }
}, $key_generation_function);
@diff = diff3(\@ancestor, \@a, \@b);
@diff = diff3(\@ancestor, \@a, \@b, $key_generation_function);
$diff = diff3(\@ancestor, \@a, \@b);
$diff = diff3(\@ancestor, \@a, \@b, $key_generation_function);
@trav = traverse_sequences3(\@ancestor, \@a, \@b, {
# callbacks
});
@trav = traverse_sequences3(\@ancestor, \@a, \@b, {
# callbacks
}, $key_generation_function);
$trav = traverse_sequences3(\@ancestor, \@a, \@b, {
# callbacks
});
$trav = traverse_sequences3(\@ancestor, \@a, \@b, {
# callbacks
}, $key_generation_function);
=head1 USAGE
This module complements L<Algorithm::Diff|Algorithm::Diff> by
providing three-way merge and diff functions.
In this documentation, the first list to C<diff3>, C<merge>, and
C<traverse_sequences3> is
called the `original' list. The second list is the `left' list. The
third list is the `right' list.
The optional key generation arguments are the same as in
L<Algorithm::Diff|Algorithm::Diff>. See L<Algorithm::Diff> for more
information.
=head2 diff3
Given references to three lists of items, C<diff3> performs a
three-way difference.
This function returns an array of operations describing how the
left and right lists differ from the original list. In scalar
context, this function returns a reference to such an array.
Perhaps an example would be useful.
Given the following three lists,
original: a b c e f h i k
left: a b d e f g i j k
right: a b c d e h i j k
merge: a b d e g i j k
we have the following result from diff3:
[ 'u', 'a', 'a', 'a' ],
[ 'u', 'b', 'b', 'b' ],
[ 'l', 'c', undef, 'c' ],
[ 'o', undef, 'd', 'd' ],
[ 'u', 'e', 'e', 'e' ],
[ 'r', 'f', 'f', undef ],
[ 'o', 'h', 'g', 'h' ],
[ 'u', 'i', 'i', 'i' ],
[ 'o', undef, 'j', 'j' ],
[ 'u', 'k', 'k', 'k' ]
The first element in each row is the array with the difference:
c - conflict (no two are the same)
l - left is different
o - original is different
r - right is different
u - unchanged
The next three elements are the lists from the original, left,
and right arrays respectively that the row refers to (in the synopsis,
these are C<@ancestor>, C<@a>, and C<@b>, respectively).
=head2 merge
Given references to three lists of items, C<merge> performs a three-way
merge. The C<merge> function uses the C<diff3> function to do most of
the work.
The only callback currently used is C<CONFLICT> which should be a
reference to a subroutine that accepts two array references. The
first array reference is to a list of elements from the left list.
The second array reference is to a list of elements from the right list.
This callback should return a list of elements to place in the merged
list in place of the conflict.
The default C<CONFLICT> callback returns the following:
q{<!-- ------ START CONFLICT ------ -->},
(@left),
q{<!-- ---------------------------- -->},
(@right),
q{<!-- ------ END CONFLICT ------ -->},
=head2 traverse_sequences3
This is the workhorse function that goes through the three sequences
and calls the callback functions.
The following callbacks are supported.
=over 4
=item NO_CHANGE
This is called if all three sequences have the same element at the
current position. The arguments are the current positions within each
sequence, the first argument being the current position within the
first sequence.
=item A_DIFF
This is called if the first sequence is different than the other two
sequences at the current position.
This callback will be called with one, two, or three arguments.
If one argument, then only the element at the given position from the
first sequence is not in either of the other two sequences.
If two arguments, then there is no element in the first sequence that
corresponds to the elements at the given positions in the second and
third sequences.
If three arguments, then the element at the given position in the first
sequence is different than the corresponding element in the other two
sequences, but the other two sequences have corresponding elements.
=item B_DIFF
This is called if the second sequence is different than the other two
sequences at the current position.
This callback will be called with one, two, or three arguments.
If one argument, then only the element at the given position from the
second sequence is not in either of the other two sequences.
If two arguments, then there is no element in the second sequence that
corresponds to the elements at the given positions in the first and
third sequences.
If three arguments, then the element at the given position in the second
sequence is different than the corresponding element in the other two
sequences, but the other two sequences have corresponding elements.
=item C_DIFF
This is called if the third sequence is different than the other two
sequences at the current position.
This callback will be called with one, two, or three arguments.
If one argument, then only the element at the given position from the
third sequence is not in either of the other two sequences.
If two arguments, then there is no element in the third sequence that
corresponds to the elements at the given positions in the first and
second sequences.
If three arguments, then the element at the given position in the third
sequence is different than the corresponding element in the other two
sequences, but the other two sequences have corresponding elements.
=item CONFLICT
This is called if all three sequences have different elements at the
current position. The three arguments are the current positions within
each sequence.
=back
=head1 BUGS
Most assuredly there are bugs. If a pattern similar to the above
example does not work, send it to <jsmith@cpan.org> or report it on
<http://rt.cpan.org/>, the CPAN bug tracker.
L<Algorithm::Diff|Algorithm::Diff>'s implementation of
C<traverse_sequences> may not be symmetric with respect to the input
sequences if the second and third sequence are of different lengths.
Because of this, C<traverse_sequences3> will calculate the diffs of
the second and third sequences as passed and swapped. If the differences
are not the same, it will issue an `Algorithm::Diff::diff is not symmetric
for second and third sequences...' warning. It will try to handle
this, but there may be some cases where it can't.
=head1 SEE ALSO
L<Algorithm::Diff>.
=head1 AUTHOR
James G. Smith, <jsmith@cpan.org>
=head1 COPYRIGHT
Copyright (C) 2003, 2007 Texas A&M University. All Rights Reserved.
This module is free software; you may redistribute it and/or
modify it under the same terms as Perl itself.