# phpman > man > Algorithm::DiffOld(3pm)

## NAME
    [Algorithm::DiffOld](https://www.chedong.com/phpMan.php/perldoc/Algorithm%3A%3ADiffOld/markdown) - Compute `intelligent' differences between two files / lists but use the old
    (<=0.59) interface.

## NOTE
    This has been provided as part of the [Algorithm::Diff](https://www.chedong.com/phpMan.php/perldoc/Algorithm%3A%3ADiff/markdown) package by Ned Konz. This particular
    module is ONLY for people who HAVE to have the old interface, which uses a comparison function
    rather than a key generating function.

    Because each of the lines in one array have to be compared with each of the lines in the other
    array, this does M*N comparisons. This can be very slow. I clocked it at taking 18 times as long
    as the stock version of [Algorithm::Diff](https://www.chedong.com/phpMan.php/perldoc/Algorithm%3A%3ADiff/markdown) for a 4000-line file. It will get worse quadratically as
    array sizes increase.

## SYNOPSIS
      use [Algorithm::DiffOld](https://www.chedong.com/phpMan.php/perldoc/Algorithm%3A%3ADiffOld/markdown) qw(diff LCS traverse_sequences);

      @lcs    = LCS( \@seq1, \@seq2, $comparison_function );

      $lcsref = LCS( \@seq1, \@seq2, $comparison_function );

      @diffs = diff( \@seq1, \@seq2, $comparison_function );

      traverse_sequences( \@seq1, \@seq2,
                         { MATCH => $callback,
                           DISCARD_A => $callback,
                           DISCARD_B => $callback,
                         },
                         $comparison_function );

## COMPARISON FUNCTIONS
    Each of the main routines should be passed a comparison function. If you aren't passing one in,
    use [Algorithm::Diff](https://www.chedong.com/phpMan.php/perldoc/Algorithm%3A%3ADiff/markdown) instead.

    These functions should return a true value when two items should compare as equal.

    For instance,

      @lcs    = LCS( \@seq1, \@seq2, sub { my ($a, $b) = @_; $a eq $b } );

    but if that is all you're doing with your comparison function, just use [Algorithm::Diff](https://www.chedong.com/phpMan.php/perldoc/Algorithm%3A%3ADiff/markdown) and let
    it do this (this is its default).

    Or:

      sub someFunkyComparisonFunction
      {
            my ($a, $b) = @_;
            $a =~ m{$b};
      }

      @diffs = diff( \@lines, \@patterns, \&someFunkyComparisonFunction );

    which would allow you to diff an array @lines which consists of text lines with an array
    @patterns which consists of regular expressions.

    This is actually the reason I wrote this version -- there is no way to do this with a key
    generation function as in the stock [Algorithm::Diff](https://www.chedong.com/phpMan.php/perldoc/Algorithm%3A%3ADiff/markdown).