Bad idea, thanks Josh

bad_diea

package Test::Calculate;
use strict;
use warnings;

use Data::Dumper;
use base 'Exporter';
use Carp qw/croak/;

our @EXPORT = ('CALCULATE');

sub CALCULATE {
    my ($struct) = @_; 
    local $Data::Dumper::Purity = 1;
    local $Data::Dumper::Useqq = 1;
    local $Data::Dumper::Deepcopy = 1;
    local $Data::Dumper::Sortkeys = 1;
    my $data = Dumper($struct);

    $data =~ s/\$VAR1 = //;
    $data =~ s/;$//;
    chomp($data);

    my @caller = caller();
    my $file = $caller[1];

    open(my $fh, '<', $file) || die "Could not open $file: $!";

    my $updated = 0;
    my @lines;
    while (my $line = <$fh>) {
        if ($line =~ m/CALCULATE/) {
            croak "CALCULATE must be called with parentheses, and must be given a scalar variable for an arg."
                unless $line =~ m/CALCULATE\(\s*\$[0-9A-Za-z_]+\s*\)/;

            $line =~ s/CALCULATE\(\s*\$[0-9A-Za-z_]+\s*\)/$data/;
        }   
        push @lines => $line;
    }   

    close($fh);
    open($fh, '>', $file) || die "Cannot open $file for writing: $!";

    print $fh @lines;

    return $struct;
}

1;