F# Tail Recursive Function Example

Question

I am new to F# and was reading about tail recursive functions and was hoping someone could give me two different implementations of a function foo - one that is tail recursi

Answer 1

I'm learning F# too. The following are non-tail recursive and tail recursive function to calculate the fibonacci numbers.

Non-tail recursive version

let rec fib = function
    | n when n < 2 -> 1
    | n -> fib(n-1) + fib(n-2);;

Tail recursive version

let fib n =
    let rec tfib n1 n2 = function
    | 0 -> n1
    | n -> tfib n2 (n2 + n1) (n - 1)
    tfib 0 1 n;;  

Note: since the fibanacci number could grow really fast you could replace last line tfib 0 1 n to
tfib 0I 1I n to take advantage of Numerics.BigInteger Structure in F#