Algorithm to determine how positive or negative a statement/text is

Question

I need an algorithm to determine if a sentence, paragraph or article is negative or positive in tone... or better yet, how negative or positive.

For instance:

<

Answer 1

   use Algorithm::NaiveBayes;
     my $nb = Algorithm::NaiveBayes->new;

     $nb->add_instance
       (attributes => {foo => 1, bar => 1, baz => 3},
        label => 'sports');

     $nb->add_instance
       (attributes => {foo => 2, blurp => 1},
        label => ['sports', 'finance']);

     ... repeat for several more instances, then:
     $nb->train;

     # Find results for unseen instances
     my $result = $nb->predict
       (attributes => {bar => 3, blurp => 2});