    note :- fib computes the n'th fibonnaci number by naive recursion
            try: fib 34?
            fibs is the list of fibonacci method by a faster method
            try: fibs 34?
            beware that fibs soon reaches integer overflow;
            
    fib n = n, n < 2
          = fib (n - 1) + fib (n - 2)

    fibs = 0:1:zipwith '+' [fibs,tl fibs]
