use strict;
use warnings;

use Engine qw( );

use constant NUM_WORKERS => 4;

sub fibonacci_task {
   my ($engine, $on_complete, $n) = @_;
   return $on_complete->(0) if $n == 0;
   return $on_complete->(1) if $n == 1;
   my ($x,$y);
   $engine->process_group(
      sub { $on_complete->($x+$y) },
      [ \&fibonacci_task => (sub { $x = $_[0] }, $n-2) ],
      [ \&fibonacci_task => (sub { $y = $_[0] }, $n-1) ],
   );
}

sub fibonacci {
   my ($engine, $n) = @_;
   my $result;
   $engine->process_and_wait(
      \&fibonacci_task => ( sub { $result = $_[0] }, $n )
   );
   return $result;
}

{
   my $engine = Engine->new(NUM_WORKERS);
   printf("%s! = %s\n", $_, fibonacci($engine, $_)) for 1..10;
}