I'm trying to take diffs between a current document and a version with a proposed change. Then the author of the document could okay or discard the changes after viewing them.

I'm working on writing an applyChange function but am having some trouble getting it to work correctly. Here's a toy script I've been playing with: 

use Data::Dumper;
use Algorithm::Diff qw(diff);
@a=qw(a b c e h j l m n p);
@b=qw(b c d e f j k l m r s t);
print "@a\n";
print "@b\n";
my $diff=diff(\@a,\@b);
while(<>){
chomp;
my(@action)=split(/ /,$_);
if($action[0] eq "+"){
      splice(@a, $action[1], 0, $action[2]);
   } elsif($action[0] eq "-"){
      splice(@a, $action[1],1);
   }


print "@a\n";
print "@b\n";
}

[download]
Then I go through and sequentially apply the "actions" within diff array from Data::Dumper which looks like so: 
$VAR1 = [
          [
            [
              '-',
              '0',
              'a'
            ]
          ],
          [
            [
              '+',
              2,
              'd'
            ]
          ],
          [
            [
              '-',
              4,
              'h'
            ],
            [
              '+',
              4,
              'f'
            ]
          ],
          [
            [
              '+',
              6,
              'k'
            ]
          ],
          [
            [
              '-',
              8,
              'n'
            ],
            [
              '-',
              9,
              'p'
            ],
            [
              '+',
              9,
              'r'
            ],
            [
              '+',
              10,
              's'
            ],
            [
              '+',
              11,
              't'
            ]
          ]
        ];

[download]
I then run my script and input the "actions" in the array above. All goes fine until the - 8 'n' command. There isn't an 'n' in location 8 at that point and it looks like we really want to take away the n at spot 9.

As I see it a number of things could be happening

  1. My splice behavior in the script is wrong
  2. I'm missing something fundamental with Algorithm::Diff's behavior and the chunks of changes
  3. Operator error running/writing the script
  4. Something weird really is going on
It's probably one or all of the first three but any help or insight would be much appreciated. 
a b c e h j l m n p
b c d e f j k l m r s t
- 0 a
b c e h j l m n p
b c d e f j k l m r s t
+ 2 d
b c d e h j l m n p
b c d e f j k l m r s t
- 4 h
b c d e j l m n p
b c d e f j k l m r s t
+ 4 f
b c d e f j l m n p
b c d e f j k l m r s t
+ 6 k
b c d e f j k l m n p
b c d e f j k l m r s t
- 8 n
b c d e f j k l n p
b c d e f j k l m r s t
- 9 p
b c d e f j k l n
b c d e f j k l m r s t
+ 9 r
b c d e f j k l n r
b c d e f j k l m r s t
+ 10 s
b c d e f j k l n r s
b c d e f j k l m r s t
+ 11 t
b c d e f j k l n r s t
b c d e f j k l m r s t


vroom | Tim Vroom | vroom@cs.hope.edu

In reply to Yet another Algorithm::Diff question by vroom

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