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coroutine0 - a working but ugly coroutine generator


  use coroutine0;
  sub one_to_N($);
  *one_to_N = new coroutine0
        VARS => [qw/$i/],
        BODY => <<'END_OF_BODY',  # single-quotes for q{} not qq{}
                $i = 1;
                while ($i < 11){
                        YIELD $i++;
        PROTO => '($)',   # gets pasted in whole: parens are required
        TIDY => 0;

  # these have their own sequences:
  *another_one_to_ten = copy {\&one_to_N} ;  #indirect
  *yet_another_one_to_ten = (\&one_to_N)->copy(); #direct

  # this one shares one_to_N's sequence:
  *same_sequence = \&one_to_N;


  coroutines using closures to provide lexical persistence


new takes a list and returns a blessed coderef. The defined argument keys include VARS and BODY. Lexicals meant to persist between calls to a routine are listed in VARS.

The new function works by rewriting each instance of /\bYIELD\b.*;/ within the body to a labeled exit/entry point and wrapping the rewritten body in an anonymous subroutine generator.

Define TIDY to a true value to suppress caching the extended coroutine source code. This breaks copy.

You can make another coroutine with its own pad by calling the copy method, which evals the wrapped body again.

define a PRE argument to include some code to run every time the coro is called, before going to the entry point.

define a DIE argument to have new tell you all about it as soon as the body is rewritten.

When the execution falls out of the bottom of the body, an undef is returned and the execution point is reset to the begining of the body. Variables are not cleared and will keep values from previous times through the routine.


$LABEL is used to store the name of the next label to jump to, so altering $LABEL in your code is dangerous, but powerful if you would like to come back in to somewhere other than directly following your exit point.

No analysis of string literals is performed, so putting YIELD in quotes within the body may cause problems if you didn't do it just to see the YIELD get expanded and printed out.

We can see package variables from the calling environment but not lexicals.


future coroutines modules might handle recursion more gracefully, might have a better declaration and definition syntax, might be a capability of a more object-oriented dispatch system rather than a clumsy hack.



VARS is now optional


Original version; created by h2xs 1.22 with options -A -C -X -b5.0.0 -ncoroutine0 --skip-exporter


Damian Conway suggested the problem

Paul Kulchenko suggested this approach when I presented a much more difficult approach to this problem at a kansas city perl mongers meeting in 2001


david nicol


Copyright 2003 by david nicol

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.