perl代码：eval＋代码的动态生成

#!/usr/bin/perl

  use strict;

  sub print_power_of_2 {
    my $x = shift;

    my $func_ref = sub {
      return $x ** 2;
    };

    my $result = &$func_ref();
    print "$x^2 = $result\n";
  }

  print_power_of_2(5);
  print_power_of_2(6);