An attempt of doing explicit lazy evaluation in perl 5 
use strict;
use warnings;
my $i = 1;
#return a pointer to a function that should be invoked
sub makeLazy { 
   my ($inp) = @_;
      sub {
         eval $inp;
      };
}
my $part2 = makeLazy('print "\nnow its $i";');
print "\ni is ".$i++;
$part2->();
print "\ni is $i";

[download]
Testing this code by 
 % test1.pl
i is 1
now its 2
i is 2

[download]
Hurray! It *seems* to work alright. But what happens when i move the declaration of $i? 
use strict;
use warnings;
#return a pointer to a function that should be invoked
sub makeLazy { 
   my ($inp) = @_;
      sub {
         eval $inp;
      };
}
my $i = 1;
my $part2 = makeLazy('print "\nnow its $i";');
print "\ni is ".$i++;
$part2->();
print "\ni is $i";

[download]
Lets give it another testrun: 
 % test1.pl
i is 1
i is 2

[download]
Eeks! Nothing happens, the $part2->() does nothing and return nothing. It doesnt even eval $i to nothing, it just does not execute! What is the cause? What is a workaround?

In reply to Not-so-lazy evaluation? by mtroost

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