Saw this and just wanted to play!

Compute.pl

#
# see http://perl.plover.com/idiocy/Addition.pm by MJD
#

use 5.014;
use warnings;

{
    package Compute;
    use Carp;

    sub AUTOLOAD {
        (my $name = our $AUTOLOAD) =~ s/^.*:://;
        
        if ($name =~ m/^startWith(\d+)/) {
            my $sum = $1;
            while ($name =~ m/(\D+)(\d+)/g) {
                given ($1) {
                    $sum += $2 when [qw/add plus/];
                    $sum -= $2 when [qw/minus subtract/];
                }
            }
            
            no strict 'refs';
            *$AUTOLOAD = sub { $sum };
            goto  &$AUTOLOAD;
        }
        
        croak "No compute!";
    }
}

say Compute->startWith10add2minus4;
say Compute->startWith12minus4minus1plus2;