You could use a list assignment in scalar context, and return an empty list to terminate. 

sub list_iter {
   my @list = @_;
   return sub {
      return @list ? shift(@list) : ();
   };
}

my $iter = list_iter('a', 1, '', 0, undef, -1);
while( my ($next) = $iter->() ) {
   print( $next // '[undef]', "\n" );
}

[download]

Another way is to populate the value using an output parameter. 

sub list_iter {
   my @list = @_;
   return sub {
      return 0 if !@list;

      $_[0] = shift(@list);
      return 1;
   };
}

my $iter = list_iter('a', 1, '', 0, undef, -1);
while( $iter->( my $next ) ) {
   print( $next // '[undef]', "\n" );
}

[download]

In both cases, the output is 

a
1

0
[undef]
-1

[download]

Update: Added second method. Removed some redundant text to "make space" for second method.

In reply to Re: Dumb, non-question: How to return 'nothing'. by ikegami
in thread Dumb, non-question: How to return 'nothing'. by BrowserUk

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