Question

I was looking at this site: http://rosettacode.org/wiki/Fibonacci_sequence#JavaScript and saw this program:

function fib(n) {
  return function(n,a,b) {
    return n>0 ? arguments.callee(n-1,b,a+b) : a;
  }(n,0,1);
}

How does this work, what are those two arguments (a and b) help. I traced it and still can’t figure out how this works

Answer 1

In the function(n,a,b), n serves as a countdown counter, and a b stores two consecutive Fibonacci numbers for the purpose of computing the next, so when n reaches 0, you have a as the n+1-th Fibonacci number (since the real Fibonacci has two 1s as the beginning).

E.g., n=4:

n  a  b
4  0  1
3  1  2
2  2  3
1  3  5
0  5  8

As you can see, the value of a and b always equal to the Fibonacci numbers. Also, this is very similar to Functional Programming (as the website stated Scheme programmers).