eratosthenes sieve

[asei-proxima]

def eratosthenes (n : Nat) : Array Bool := Id.run do
  let mut isPrime := Array.mkArray (n + 1) true

  isPrime := isPrime.set! 0 false
  isPrime := isPrime.set! 1 false

  for p in [2 : n + 1] do
    if not isPrime[p]! then
      continue

    let mut q := 2 * p
    while q <= n do
      isPrime := isPrime.set! q false 
      q := q + p

  return isPrime

def runTest (n : Nat) : IO Unit := do
  let l := eratosthenes n
  for i in [:l.size] do
    if l[i]! then
      IO.print s!"{i} "

#eval runTest 19