If I had the push, I would put coroutines or at least iterators into the Perl 5 core, like Coro provides them already (in a less portable, more restricted way). With at least iterators, you can easily avoid the "inversion of control" problem that arises as soon as you have or use a framework that either provides callbacks or provides call-in hooks, and you don't need to maintain state yourself (see the push/pull examples below).
Painless iterators:
sub i_produce {
my ($start, $count) = @_;
for my $i ($start..$start+$count) {
yield $i;
};
};
sub i_two_columns {
while (defined (my $i = produce)) {
print $i;
if (defined (my $j = produce)) {
print "\t$j";
};
print "\n";
};
};
Perl way (push):
sub p_produce {
my ($consumer, $start, $count) = @_;
for my $i ($start..$start+$count) {
$consumer->($i);
};
};
{
my $odd;
sub p_two_columns {
# aieeee - need to maintain state
$odd = ($odd + 1)%2;
};
};
Perl way (pull):
{
sub p_produce {
my ($consumer, $_start, $_count) = @_;
# aieee - need to maintain state:
my $pos = $start;
return sub {
$pos < $start+$count ? $pos++ : undef
};
};
};
sub i_two_columns {
my ($produce) = p_produce(2,10);
while (defined (my $i = $produce->())) {
print $i;
if (defined (my $j = $produce->())) {
print "\t$j";
};
print "\n";
};
};
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