Generating Fibonacci series in F#

Question

I\'m just starting to learn F# using VS2010 and below is my first attempt at generating the Fibonacci series. What I\'m trying to do is to build a list of all numbers less

Answer 1

Yes, mutable variables and while loops are usually a good sign that your code is not very functional. Also the fibonacci series, doesn't start with 1,2 - it starts with 0,1 or 1,1 depending on who you ask.

Here's how I'd do it:

let rec fabListHelper (a:int,b:int,n:int) =
  if a+b < n then
    a+b :: fabListHelper (b, a+b, n)
  else
    [];;

let fabList (n:int) = 0 :: 1 :: fabListHelper (0,1, n);;

(*> fabList 400;;
val it : int list = [0; 1; 1; 2; 3; 5; 8; 13; 21; 34; 55; 89; 144; 233; 377]*)