import Data.List (find)

isqrt :: (Integral n) => n -> n
isqrt = floor . sqrt . fromIntegral

isPrime :: (Integral n) => n -> Bool
isPrime n = (n >= 2) && all ((/= 0) . (n `mod`)) [2 .. isqrt n]

goldbach :: (Integral n) => n -> (n, n)
goldbach n =
  if odd n
    then error "Odd number was given"
    else (p, n - p)
  where
    Just p = find (\p -> (n - p) `elem` primes) primes
    primes = filter isPrime [2 .. n - 1]

goldbachList' :: (Integral n) => n -> n -> n -> [(n, n)]
goldbachList' m n d = filter (\(p, q) -> p > d && q > d) $ map goldbach $ filter even [m .. n]

goldbachList :: (Integral n) => n -> n -> [(n, n)]
goldbachList m n = map goldbach $ filter even [m .. n]