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copied!<p>There is a similar method to produce a Iterator / Generator, but it is not a "first class citizen" as it is on Python.</p> <p>In Perl, if you do not see what you want (after a <strong>MANDATORY</strong> trip to <a href="http://search.cpan.org/search?query=iterator&mode=all" rel="noreferrer">CPAN</a> <strong>FIRST</strong>!), you can roll your own that is similar to a Python iterator based on Perl closures and an anonymous subroutine. </p> <p>Consider:</p> <pre><code>use strict; use warnings; sub fibo { my ($an, $bn)=(1,0); my $mag=(shift || 1); my $limit=10**$mag; my $i=0; return sub { ($an, $bn)=($bn, $an+$bn); return undef if ($an >=$limit || wantarray ); return $an; } } my $num; my $iter=fibo(15); while (defined($num=$iter->()) ) { printf "%17d\n", $num; } </code></pre> <p>The sub <code>fibo</code> maintains a Perl <a href="http://perldoc.perl.org/perlfaq7.html#What's-a-closure%3f" rel="noreferrer">closure</a> that allows persistent variables to be maintained. You can do the same by having a module, similar to C / C++. Inside <code>fibo</code> an anonymous subroutine does the work of returning the next data item. </p> <p>To quote from the <a href="http://rads.stackoverflow.com/amzn/click/0596000278" rel="noreferrer">Perl Bible</a> "You will be miserable until you learn the difference between scalar and list context" -- p 69 (A highly recommended book btw...)</p> <p>In this case, the annon sub only returns a single value. The only looping mechanism that I know of in Perl that can work in scalar context is <code>while</code>; The others try to fill the list before proceeding I think. Therefor, if you called the anon sub in list context, it will dutifully return the next fibonacci number, unlike Python's for iterators, and the loop would terminate. That is why I put the <code>return undef if .... wantarray</code> because it does not work in list context as written. </p> <p>There are ways to fix that. Indeed, you can write subroutines that act like <code>map</code> <code>foreach</code> etc but it is not as straightforward as Python's yield. You will need an additional function to use inside a foreach loop. The tradeoff is the Perl approach has tremendous power and flexibility. </p> <p>You can read more about Perl iterators in Mark Jason Dominus' excellent book "Higher Order Perl" <a href="http://hop.perl.plover.com/book/pdf/04Iterators.pdf" rel="noreferrer">Chapter 4 is all about Interators</a> brian d foy also has an excellent <a href="http://www.theperlreview.com/Articles/v0i5/iterators.pdf" rel="noreferrer">article</a> on Interators in the Perl Review.</p>

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