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Generating Fibonacci series in F#

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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 than 400.

let fabList = 
    let l =  [1;2;]
    let mutable a = 1
    let mutable b = 2
    while l.Tail < 400 do
        let c = a + b
        l.Add(c)
        let a = b
        let b = c

My first problem is that on the last statement, I'm getting an error message "Incomplete structured construct at or before this point in expression" on the last line. I don't understand what I'm doing wrong here.

While this seems to be an obvious way to build the list in a fairly efficient way (from a c++/C# programmer), from what little I know of f#, this doesn't seem to feel to be the right way to do the program. Am I correct in this feeling?

like image 689
photo_tom Avatar asked May 16 '10 22:05

photo_tom


1 Answers

Other posts tell you how to write the while loop using recursive functions. This is another way by using the Seq library in F#:

// generate an infinite Fibonacci sequence
let fibSeq = Seq.unfold (fun (a,b) -> Some( a+b, (b, a+b) ) ) (0,1)
// take the first few numbers in the sequence and convert the sequence to a list
let fibList = fibSeq |> Seq.takeWhile (fun x -> x<=400 ) |> Seq.toList

for explanation, please ref solution 2 in F# for Project Euler Problems, where the first 50 Euler problems are solved. I think you will be interested in these solutions.

like image 73
Yin Zhu Avatar answered Sep 25 '22 14:09

Yin Zhu