Lazy prime numbers in Haskell

lazy_primes.hs

sqrti x = (truncate . sqrt . fromInteger) x
primes = filter (\n -> all (\y -> n `mod` y /= 0) [2..sqrti(n)]) [2..]
isPrime x = elem x (takeWhile (<= x) primes)
 
-- ghci> take 10 primes
-- [2,3,5,7,11,13,17,19,23,29]
-- ghci> take 8 (drop 2 primes)
-- [5,7,11,13,17,19,23,29]
-- ghci> take 100500 primes
-- ...
-- ghci> isPrime 1
-- False
-- ghci> isPrime 2
-- True
-- ghci> isPrime 3
-- True
-- ghci> isPrime 16
-- False
-- ghci> isPrime 31
-- True

Ruby version here