• Break the code between the yields into code refs
• Create a dispatch table that knew about all the sections
• Create a tied variable that knows how to cycle through the dispatch table
• Return a closure calling the dispatch table

package Iterator;
sub TIESCALAR { bless $_[1], $_[0] }
sub STORE {}
sub FETCH { $_[0]->[1] = 0 if ! $_[0]->[1] || $_[0]->[1] == @{ $_[0]->
+[2] }; $_[0]->[1]++ }

package Coroutine;
sub new {
    my $self = bless [[[]]], $_[0];
    tie $self->[0][0], 'Iterator', $self->[0];
    return $self;
}
sub add_section { push @{ $_[0]->[0][2] } , $_[1] }
sub create { my $s = shift; return sub { $s->[0][2][ $s->[0][0] ]->($s
+, @_) } }
42;
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#!/usr/bin/perl
use strict;
use warnings;
use Coroutine;

my $coroutine = Coroutine->new();
$coroutine->add_section(
    sub {
        my $self = shift;
        $self->[3] = shift;
        $self->[4] = \@_;
        print "$_\n" for @{ $self->[4] };
        return $self->[3]++;
    }
);

$coroutine->add_section(
    sub {
        my $self = shift;
        print "$self->[3]\n";
        return rand() > .5 ? 'weird' : ++$self->[3];
    }
);

$coroutine->add_section(
    sub {
        my $self = shift;
        print "The end is near - goodbye cruel ";
        return pop @{ $self->[4] };
    }
);

my $wacky = $coroutine->create(42, 'hello', 'world');
print $wacky->(42, 'hello', 'world'), "\n";
print $wacky->(), "\n";
print $wacky->(), "\n";
print $wacky->(), "\n";
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coroutine create {
    my $foo = shift;
    my @bar = @_;
    print "$_\n" for @bar;
    yield $foo++;
    print "$foo\n";
    yield rand() > .5 ? 'weird' : ++$foo;
    print "The end is near - goodbye cruel ";
    yield pop @bar;
}
my $wacky = create(42, 'hello', 'world');
print $wacky->(42, 'hello', 'world'), "\n";
print $wacky->(), "\n";
print $wacky->(), "\n";
print $wacky->(), "\n";
__END__
hello
world
42
43
44|weird
The end is near - goodbye cruel world
0
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