Simple Prime Sieve

PrimeSieve.hs

data Sieve = Sieve
   { limit :: Int
   , position :: Int
   , product :: Int
   , sieve :: [Int]
   , count :: Int
   } 

uniquePrimes :: Sieve -> Maybe (Int, Sieve)
uniquePrimes (Sieve limit position product sieve count) = if product * position > limit
    then Nothing
    else if isPrime position
        then let count' = count + 1
                 product' = product * position
              in Just $ (count', Sieve limit position' product' (position : sieve) count')
        else uniquePrimes $ Sieve limit position' product sieve count
  where
    position' = position + 1
    isPrime c = not $ any (\p -> c `mod` p == 0) sieve