#!/usr/bin/perl -w
use strict;
use Data::Dumper;
use String::Approx qw\amatch\;
use Benchmark 'cmpthese';

#----------Begin Benchmarking--------------

my $str = 'AAAAA';
my @arr = ('AAAAA','ATAAA','ATCGA','ATCAA');

my @my_match = mymatch($str,2,\@arr);
print Dumper \@my_match;

my @jk_match = amatch($str,['2'],@arr);
print Dumper \@jk_match;

#It fails here
cmpthese (-5,{ me => "mymatch($str,2,\@arr)",
               jk => "amatch($str,['2'],@arr)",});

#------------------ Subroutine -------------
sub mymatch {

    my ($pattern, $d, $arr_2match) = @_;
    my @matches;

    foreach (@$arr_2match){
        my $diff = hd($pattern,$_);
        #print "$_ --- Diff: $diff\n";

        if ($diff <= $d){
            push @matches, $_;
        }       
    }
    return @matches;
}

sub hd {
        #String length is assumed to be equal
        my ($a,$b) = @_;
        my $len = length ($a);
        my $num_match=0;

        for (my $i=0; $i<$len; $i++) { 
        # assume that the lists are of same length
          ++$num_match if substr($a, $i, 1) ne substr($b, $i, 1);
        }

        return $num_match;
}
[download]

Such that it gives this result:

[snip others]
Can't locate object method "ATCGA" via package "ATCAA" 
(perhaps you forgot to load "ATCAA"?) at (eval 7) line 1.
[download]

Is Benchmark only cater for Perl written subroutine/module? Is there a way to overcome it?