CODEWITHSUNDEEP
f#
BabaBert
BabaBert

Reputation: 141

FS0001 Should be "int32", is "unit" instead

First of all, I am a complete beginner to functional programming and F#. I am kinda getting into the basic concepts and I tried to start practicing my understanding by writing a Mandelbrot set program. The function iterate should take a tuple, iterate over it, and in case the exit condition infinity is med, it should return the amount of iterations i it took. Else it calls itself with the changed tuple. I receive the following error: FS0001 Should be "int32", is "unit" instead line 2

Edit: mandelbrot takes a tuple and return a tuple; infinity takes a tuple and return an integer

let rec iterate (a, b) :int32 = 
    for i:int32 in 0..100 do 
        (a, b)
        |> mandelbrot
        |> match infinity with
            | a when a > 16 -> i
            | a when a <= 16 -> iterate (a, b)

Upvotes: 0

Views: 84

Answers (2)

BabaBert
BabaBert

Reputation: 141

Before I try to explain the function unnecessarily here is how the code would look like written in C:

int iterate(int a, int b) { int i, ca = a, cb = b, aa, bb;

for (i = 0; i <= 100; i++) {
    aa = a * a - b * b;     //mandelbrot algorithm
    bb = 2 * a * b;
    a = aa + ca;
    b = bb + cb;

    //checks if the the values deviate to infinity
    if ((a + b) > 16) { 
        return i;
    }
}

}

I thought about using recursion but since Iam not used to the functional paradigm I tried to avoid it for efficiency reason and basically tried to create a break condition. Turns out, F# compiles tail recursion into while loops so all this was just really unnecessary and dumb. https://gist.github.com/mrange/3a275cc643c9753925f1c8a68b0bd7a0

Still hope it helps someone and thanks for everyone that tried to make sense out of the code I wrote.

Upvotes: -1

Koenig Lear
Koenig Lear

Reputation: 2436

It's hard to guess what you want to achieve. However a few tweaks could get you to compile. A for do expects a function returning unit e.g. a statement.

If you want go through iterate up to a hundred times you could use a variable i that you pass inside the iteration and you increase it each time you make a call and initialize it with 0 e.g. iterate (2,3) 0

let mandelbrot (a,b) = (a,b)

let infinity (a,b) = a


let rec iterate (a, b) i :int = 
        (a, b)
        |> mandelbrot
        |> infinity 
        |> (fun a-> if i=100 then a else
                    match a with
                      | a when a > 16 ->  i
                      | _ ->  iterate (a,b) (i+1))

Upvotes: 2

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