Nix: Dynamic Fibonnaci in Functional Style O(n)

dynamic_fibonnaci.nix

let
    fib = number: fib' number 1 1;
    fib' = number: first: second:
        if number == 0
        then first
        else fib' (number - 1) second (first + second);
        # the second becomes the new first, the (first + second) becomes the new second
in
    fib 5