playPrng.fs

let twister (n: float) = 
    let n = min n 100.
    let n = max 0. n
    let a = n * 2.
    //if a < 50 then 1 else 0
    let a' = 
        let x = min (n-50.) 0.
        let y = min -x 1.
        y
    let b = (100. - n) * 2.
    //if a >= 50 then 1 else 0
    let b' = 
        let x = max 0. (n - 50.)
        let y = min 1. x
        y
    a' * a + b * b'
let cyclicTwister (n: int) = 
    let n = min n 100
    let n = max 0 n
    let a = n * 2
    //if a < 50 then 1 else 0
    let a' = 
        let x = min (n-50) 0
        let y = min -x 1
        y
    let b = (100 - n) * 2
    //if a >= 50 then 1 else 0
    let b' = 
        let x = max 0 (n - 50)
        let y = min 1 x
        y
    a' * a + b * b'
let inline ap (f: 'a -> 'a) a i = 
    let rec ap' a i = 
        match i with
        | 0 -> a
        | n -> ap' (f a) (i-1)
    ap' a i

let twist = ap twister >> Seq.initInfinite
let cycTwist  = ap cyclicTwister >> Seq.initInfinite 
//gets the "length" of the infinite sequence
let inline grab (m: 'a seq) =
    let rec grab' seen l' = 
        let head = Seq.head l'
        if seen |> Seq.contains head |> not then
            grab' (head::seen) (l' |> Seq.tail)
        else
            seen
    grab' [Seq.head m] (m |> Seq.tail)

let inline len (l: 'a seq) = grab l |> Seq.length
    
[1..100] |> List.map (cycTwist >> len)