sidef/scripts/RosettaCode/fibonacci_sequence_3.sf

#!/usr/bin/ruby

#
## https://rosettacode.org/wiki/Fibonacci_sequence
#

func fib_closed(n) {
    define S = (1.25.sqrt + 0.5);
    define T = (-S + 1);
    (S**n - T**n) / (-T + S) -> roundf(0);
}

say fib_closed(12);