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Creating an endless set of numbers

I am trying to create a prime number generator that should be able to return a sequence of primes up to the nth number. Now I figured there must be a more elegant way to do this with sequences, other than my current solution, which looks a little verbose, and I had to use mutables.

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|> Seq.unfold (fun x -> if isPrime x 
                          then Some(x, x + 1) 
                         else 
                          let mutable y = x
                          while isPrime y <> true do
                           y <- y + 1
                          Some(y, y + 1)) 
|> Seq.take(n)
+3


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2 answers


Simple solution using a filter



let t = Seq.initInfinite id |> Seq.filter isPrime |> Seq.take n
+5


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just for completeness see this MSDN sequence handling . It includes this definition of isPrime



let isPrime n =
    let rec check i =
        i > n/2 || (n % i <> 0 && check (i + 1))
    check 2

let t2 n = seq { for n in 1..100 do if isPrime n then yield n } 
t2 10
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