Fibonnaci in F# [closed]

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this que开发者_如何学Cstion so that it can be reopened, visit the help center. Closed 10 years ago.

with the multiple assignment (ie a,b=b,a) in f# its possible to write Fibonacci in a single line .. Can some one show how it is .. i know its possible in ruby

---

Longer but much faster version (via tail recursion in auxiliary function fibi):

let fib = let rec fibi a b = function | 0 -> a | c -> fibi b (a+b) (c-1) in fibi 0I 1I

---

Scott Hanselman pretty much covers this in this blog post.

Here is the relevant snippet:

let rec fib n = if n < 2 then 1 else fib (n-2) + fib(n-1)

Scott got that from Dustin Cambell's blog. I post Scott's version because he also has the Ruby code for it. It's worth noting that in F#, variables are generally immutable so a,b = b,a is not actually reassigning anything (I don't think it's even valid syntax). Rather, a function like let swap (a,b) = (b,a) is taking a tuple and returning a new tuple with the contents reversed.

---

For the uninitiated, Seq.unfold is a sequence generator. It accepts as seed as input and invokes a function which returns the next element in the sequence as Some(nextElement, nextSeed), or None to terminates the sequence.

It makes for a very interesting fibonacci one-liner:

> let fibs = (0L, 1L) |> Seq.unfold (fun (a, b) -> Some(a, (b, a+b)));;

val fibs : seq<int64>

> fibs |> Seq.take 50 |> Seq.toList;;
val it : int64 list =
  [0L; 1L; 1L; 2L; 3L; 5L; 8L; 13L; 21L; 34L; 55L; 89L; 144L; 233L; 377L; 610L;
   987L; 1597L; 2584L; 4181L; 6765L; 10946L; 17711L; 28657L; 46368L; 75025L;
   121393L; 196418L; 317811L; 514229L; 832040L; 1346269L; 2178309L; 3524578L;
   5702887L; 9227465L; 14930352L; 24157817L; 39088169L; 63245986L; 102334155L;
   165580141L; 267914296L; 433494437L; 701408733L; 1134903170L; 1836311903L;
   2971215073L; 4807526976L; 7778742049L]

---

let main = System.Console.WriteLine("Fibonacci")