The Haskell code can be slightly simplified to nth :: Integral a => Int -> Maybe a nth n | n < 1 = Nothing | True = Just (primes !! (n-1))

The Haskell code can be slightly simplified to nth :: Integral a => Int -> Maybe a nth n | n < 1 = Nothing | True = Just (primes !! (n-1)) primes :: Integral a => [a] primes = sieve [2..] where sieve (p:xs) = p : sieve [x | x <- xs, x `mod` p /= 0] Note that this is not a genuine sieve [1] [1] https://www.cs.hmc.edu/~oneill/papers/Sieve-JFP.pdf https://www.cs.hmc.edu/~oneill/papers/Sieve-JFP.pdf