[StackOverlord]

You can also recursively define fib as a lazy sequence that is the pairwise sum of fib and fib shifted by one. (Clojure, from Rosetta Code).

    (def fib (lazy-cat [0 1] (map + fib (rest fib))))

    => (take 10 fib)
    (0 1 1 2 3 5 8 13 21 34)


    Explanation:

       0 1 1 2 3 5   ;  this is fib
    +  1 1 2 3 5 8   ;  this is (rest fib) 
    ---------------
       1 2 3 5 8 13  ;  this is (map + fib (rest fib))
                     ;  and the sequence needs to be initialized with (lazy-cat [0 1] ...