(* sum all integers from 1...n *)
let sum_from_one n =
   let rec aux n sum =
      if n > 0
      then aux (n - 1) (sum + n)
      else sum
   in aux n 0

(* int list of fibonacci numbers of length n *)
let fibs_list n =
   let rec aux a b l =
    if List.length l = n then l
    else aux b (a+b) (b::l)
   in List.rev (aux 0 1 []);;