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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"; }; };

In reply to Re: (Sort of) poll: what Perl6 features do you consider {likely,desirable} to leak into P5? by Corion
in thread (Sort of) poll: what Perl6 features do you consider {likely,desirable} to leak into P5? by blazar

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