check overload 
#!perl
use strict;
use warnings;

my $num = new SomeThing 57;
    $b=5+$num;
    print "b is $b \n";
    my $minus = $num - 10;
    print "minus is $minus \n";


package SomeThing;

 sub new { my $p = shift; bless [@_], $p }
use overload
    '+' => \&myadd,
    '-' => \&mysub;

sub myadd {
    my $self = shift;
    my $var = shift;
    return ($var + $self->[0]);
}

sub mysub {
    my $self = shift;
    my $var = shift;
    return ( $self->[0] - $var);
}
1;

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In reply to Re: string to expression by mkirank
in thread string to expression by xiaoyafeng

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