multi fsum([] , UInt ) { Empty }
multi fsum([UInt $first, *@rest], UInt $num where * < $first) { Empty }
multi fsum([UInt $first, *@rest], UInt $num where * == $first) { [[ $first, ],] }
multi fsum([UInt $first, *@rest], UInt $num where * > $first) {
[|fsum(@rest, $num), |fsum(@rest, $num - $first).map: -> @seq { [$first, |@seq] } ]
}
sub fibonacci-sum($sum) {
my @fib = 1, 2, &[+] ... *;
my $f = @fib.first: * > $sum;
fsum @fib[^$f], $sum
}
for ^20 {
say .sum, " == ", .join(" + ") for fibonacci-sum $_
}
