Your Haskell code doesn't quite parse. But the following works: import Data.List primes = Data.List.nubBy (\a b -> gcd a b > 1) [2..] findTwins pri

Your Haskell code doesn't quite parse. But the following works: import Data.List primes = Data.List.nubBy (\a b -> gcd a b > 1) [2..] findTwins primes = [(p,q) | (p:q:_) <- tails primes, q == p+2] main = mapM_ print . take 10 . findTwins $ primes Finding primes arbitrarily far apart can be done in Haskell as findBigTwins gap primes = [(p,q) | (p:qs) <- tails primes, let q = p+gap, q `elem` takeWhile (<= q) qs]