use strict;
use warnings;

my $helloWorld = sub{return "Hello world 1"};

process($helloWorld);
process(sub{return "Hello world 2"});
process(\&helloWorld);
process(sub{return $_}) for 1 .. 5;
process(sub{mul10($_)}) for 1 .. 5;



sub helloWorld {
      return "Hello World 3";
}


sub mul10 {
   my ($x) = @_;
   
   return $x * 10;
}


sub process {
   my ($callback) = @_;
   
   print $callback->(), "\n";
}