#! perl -slw
use strict;
use futures;

sub fibonacci {
    my $n = shift;
    return $n if $n < 2;
    my $r1 = futures->new( \&fib_t1, $n -2 );
    my $r2 = futures->new( \&fib_t1, $n -1 );
    return $r1 + $r2;
}

sub fib_t1 {
    my $n = shift;
    return $n if $n < 2;
    my $r1 = futures->new( \&fib_t2, $n -2 );
    my $r2 = futures->new( \&fib_t2, $n -1 );
    return $r1 + $r2;
}

sub fib_t2 {
    my $n = shift;
    return $n if $n < 2;
    return fib_t2( $n -2 ) + fib_t2( $n -1 );
}


printf "$_ : %d\n", fibonacci( $_ ) for 1 .. $ARGV[ 0 ];

__END__
C:\test>885839-t 20
1 : 1
2 : 1
3 : 2
4 : 3
5 : 5
6 : 8
7 : 13
8 : 21
9 : 34
10 : 55
11 : 89
12 : 144
13 : 233
14 : 377
15 : 610
16 : 987
17 : 1597
18 : 2584
19 : 4181
20 : 6765